300 RUM load development questions

[Lefty7mmstw]

I'd suggest using a slightly faster powder than Retumbo. In similar size cases used in competition, IMR4350 or others at that speed (VV550 or Re-17, too) typically produce much better accuracy. But the compromise is bullets leaving 50 to 100 fps slower. So one has to choose between more accuracy or more power on target at long range. Rarely does one get both.

Yep, the accuracy is usually better as the muzzle pressure is lower. But, the 300 rum and 7 stw are nearly identical in their overbore nature, and as the graphs I posted on the 4000 fps stw thread indicate, the KPSI at the muzzle is only around 10,000 with a rl25 speed powder, so I doubt you will see more than 1 or 2 KPSI drop in pressure with a 4350 type powder. With a mid-mag like a 7rem or 300 win this is a very good way to play, but as overbore as we are here I get more worried about open space in the case than a slightly lower muzzle pressure.

 

[Bart B]

If using a bushing die will I need to neck size down more than once? I guess maybe my chamber dimensions will determine that. I did talk to Redding about bushing dies, and they said that you cant bush down more than. .005 without having concentricity problems. If more sizing than that is needed bushing down more than once may be required.

I'm on a new Hart barrel, and like I said I dont know the details of the chamber. So far it appears to be fairly tight. I'll measure some neck diameters after firing and see exactly how much sizing is needed. That I have not done yet.
When I stuck the case I was experimenting more anything, and was just bushing down a fired case with a concentric nech to. .336 and then check to see if that gave me any concentricity problems.

Anyway, it sounds like experimenting will be further needed before I just start throwing ammo together. My first rounds were easy as the Nosler brass was already sized and concentric. Now I'll see what sizing operations are going to give me the best results.

I'm a believer that reamers that make tight chamber necks and neck only sizing dies are best used as door stops, paper weights or in ammo for large bore shotguns.

Most anything that goes through the inside of a sized down case neck will bend it off its sized axis a full length bushing die positioning it perfectly. At least on all the ones I've measured. Use a bushing diamter that make case neck tension what you want.

It doesn't matter how much neck clearance there is on bottleneck cases headspacing on their shoulder. As the round's shoulder is perfectly centered in the chamber shoulder when fired, it's the off-center misalignment of case necks on case shoulders that causes problems. Proper use of full length dies without expanders makes case necks better centered on case shoulders than neck only sizing dies. Neck only dies do not hold the case body well aligned with its neck sizing hole.

After all, a chambered round's neck doesn't touch the chamber neck anyway when the round's fired so why all the need for tight neck chambers? The only time a case neck might touch the chamber neck is after the bullet's left the case mouth and well into the rifling.

 

[MontanaRifleman]

Hey Montana and Bart, I got rid of the expander ball, and have tried a couple different methods. My runout problem is solved. Firct off, I replaced my case holder, then sized without expander ball, then Sinclair expander die for consistent neck tension. This leaves me with little to no runout. Almost forgot, I got a VLD seater plug. I think that was the biggest part of my problem. Also getting no runout issues with a Redding bushing die. Thats what I'm using.
I've done a little testing with 210 VLD, and surprisingly for starters at 88 gr Retumbo to get centered on target for further testing, I shot just over 3/4"group at 200 yds. This was with virgin Nosler brass.
I have some further test loads ready to go. I'm loading at. .010 off lands. It seems to like the 210 VLD's. I'd like you guy's opinion as to where to go from here.

Good news cerwin! Did you determine the shell holder was part of the problem?

The expander die sounds like a good step. My question is, if the necks are not turned then won't the bushing die push any irregularities back in? Maybe your necks are turned? Can't remember. Sounds like great results on the range. Whatever you're doing, it's working.

And yes, the VLD seating plug is a good idea. I'll be doing the same with all my seaters.

 

[Tidesloe]

Good news cerwin! Did you determine the shell holder was part of the problem?

The expander die sounds like a good step. My question is, if the necks are not turned then won't the bushing die push any irregularities back in? Maybe your necks are turned? Can't remember. Sounds like great results on the range. Whatever you're doing, it's working.

And yes, the VLD seating plug is a good idea. I'll be doing the same with all my seaters.

Rifleman,
The case holder, I'm not completely sure if it was a part of the problem, but that was just one of steps. I only suspected that it could be a contributor.
Im using Nosler brass, and after measuring case neck thickness they seem pretty consistent, so the expander die was more of a step to be sure that any irregularities are moved back out, and I have consistent neck tension. Separately using the expander die did not produce any concentricity issues. I measured everything for concentricity after each step. Part of it is my curiosity in to what the various methods produce. I'm still experimenting, and going broke doing it. In the end I can probably get the same results, possibly even better results with fewer steps, as I think Bart may have alluded to above.
My standard seater plug was the problem, for the most part. Took it out and inserted a VLD, and the tip would bottom out, and bullet wobbled around. After seating VLD's with the standard plug, I couldn't even chamber the rounds. I got a VLD seater plug, and it seats VLD's straight, with on avg. .001 runout.
I'm learning more and more every day, and seem to have found a way thats working, as far as sizing and seating. Bart, I do have a FL bushing die, and may have no need to separately expand. The Nosler cases have measured consistently in the neck.

This RUM will become my backup gun by the end of next month. I done went off the deep end, and bought a fully custom built 7 STW. I'd like to have a known and proven load for the RUM before that time. I think the group I shot to get centered on target is coincidental. What are the chances that my starting charge would shoot that well? Apparently pretty good, but I believe there is something at the upper end that will do as well. It gives me hope that I'm on to something. I've worked on an Accubond load with it, and could not get anything to shoot as well as the VLD's seem to be shooting.

As far as the faster, slower powders go, I'm still a little green to worry about that. I understand the concept, but I think only experience with the different powders, and their burn rates affect on different bullet weights will be needed. I do however appreciate all of the suggestions and knowledge shared. I would hope to be at that level of knowledge and skill someday. You guy's are helping with that already. Thanks!!!

Anyway, when the STW gets here next month my only LR scope will be coming off the RUM and going on the STW. Between now and then I plan on doing a ladder test to get a bit warmer load in the node, hopefully. I'll get back with you guy's with results.

Thanks

 

[Tidesloe]

Yep, the accuracy is usually better as the muzzle pressure is lower. But, the 300 rum and 7 stw are nearly identical in their overbore nature, and as the graphs I posted on the 4000 fps stw thread indicate, the KPSI at the muzzle is only around 10,000 with a rl25 speed powder, so I doubt you will see more than 1 or 2 KPSI drop in pressure with a 4350 type powder. With a mid-mag like a 7rem or 300 win this is a very good way to play, but as overbore as we are here I get more worried about open space in the case than a slightly lower muzzle pressure.

I have actually tried IMR 4350 with 180 Accubonds. I did a round robin test with it, might be better at 200 gr. bullets. It shot well, but not as well as the VLD's at my start charge of 88 gr. Retumbo. I chose Retumbo for it's temp insensitive nature, and after reading that IMR powders tend to be more temp sensitive. I'm loading a hunting round.
So, are you saying that accuracy may suffer at higher pressure loads? My start charge is plenty accurate. 3/4" 200 yd. group! I've never shot groups like that before. I'm new to LR, and I've spent the last 40 yrs looking for that type of accuracy in factory rifles, and factory ammo only to learn after all these years that it aint likely. At least for me it hasn't been. Now with custom rifles, and producing my own ammo, I clearly see its very possible. EVEN for me.

Having not chrono'd anything yet, I know that the 88 gr load is not gonna have the velocity I'm looking for, and would like to find something at the upper end that does as well. Thats part of the puzzle that I need to be implementing. In the end I would give up some velocity for accuracy.

I just bought a custom 7 STW, with load development and testing already done. I'll have that rifle next month. The load for it is using Vihtavouri N570, 180 gr. VLD's. I suspect that would work well for my RUM as well. I already have some on hand, just got it yesterday. Do you guy's have any experience with Viht 500 series powders?

 

[Bart B]

Cerwin, I think you're moving in the right direction.

My (and so darned many others) facination with full length sizing dies without expander balls is based on what the benchresters learned a few years ago. The size of benchrest smallest groups shot with a given load are not any smaller. But the size of the largest groups are smaller; 30% to 50% smaller. Benchrest group aggregates got smaller. It's sort of like deciding if you'll accept groups from 1 to 6 units of measure or 1 to 4.

Regarding neck wall irregularities being pushed to the inside and left there without an expander ball pushing them out. . . . . They're pushed back out to exactly bullet diameter when the bullet's seated. A half thousandth spread in neck wall thickness will cause a 1/2 thousandth spread in outside diameters measured around the case neck. That's not a problem. There a small amount of case neck positioning in the chamber neck while pressure builds up in the case body before the bullet gets pushed out.

 

[RTK]

The last few years I have not been using any expander balls in any of my sizing dies (neck & FL). They do over size the necks to a slightly smaller diameter but that hasn't affected anything that I can tell. The run out is much smaller and it makes me sleep better at night.......................

 

[Tidesloe]

Cerwin, I think you're moving in the right direction.

My (and so darned many others) facination with full length sizing dies without expander balls is based on what the benchresters learned a few years ago. The size of benchrest smallest groups shot with a given load are not any smaller. But the size of the largest groups are smaller; 30% to 50% smaller. Benchrest group aggregates got smaller. It's sort of like deciding if you'll accept groups from 1 to 6 units of measure or 1 to 4.

Regarding neck wall irregularities being pushed to the inside and left there without an expander ball pushing them out. . . . . They're pushed back out to exactly bullet diameter when the bullet's seated. A half thousandth spread in neck wall thickness will cause a 1/2 thousandth spread in outside diameters measured around the case neck. That's not a problem. There a small amount of case neck positioning in the chamber neck while pressure builds up in the case body before the bullet gets pushed out.

Thats awesome!, more consistency (smaller aggregates) is exactly my goal.

I agree with you on the neck irregularities being pushed back out with bullet seating, and that it doesn't matter, as the necks dont contact the chamber walls when fired anyway. but I do ask if these slight irregularities in the necks after sizing and pushed to the inside of neck can cause a slight irregularity in neck tension leading to decreased accuracy? Hope I'm not sounding like a smart _ _ _ here. I'm very green in this pursuit, and just have many questions. Im completely open to all your input. I depend on you guy's with knowledge and experience. I want to eliminate all variables I can, but then the issue of a separate expanding operation with a separate die has the potential to cause concentricity problems as well. It is more steps, and another potential to produce a problem, but I haven't seen a problem there yet. Possibly in the end it amounts to six in one hand, and half a dozen in the other, and I eliminate the neck expanding. I dont know anything for sure yet other than I have a lot to learn.
I couldn't do it without you, and the other guy's willing to share their experience.
I could use an opinion on further testing. I would like to do a ladder test, but only have access to a 200 yd range, without traveling a couple of hours, or packing all my gear a couple miles back into the Natl Forest. Would a round robin type test at 200 be a resonable method? If so, do you have any advice or suggestions?
Thanks again, I'll definitely be back in touch

 

[Bart B]

but I do ask if these slight irregularities in the necks after sizing and pushed to the inside of neck can cause a slight irregularity in neck tension leading to decreased accuracy?

Good question.

Military match ammo (M118 and M852 7.62 NATO stuff as well as M72 .30-06) has a release force (neck tension, in MIL SPEC terms) of at least 40 pounds. Some of the stuff I've measured has a 10 to 15 pound spread above that. But it still shoots 7 inches at 600 yards with bullets not as good as Sierra's match bullets. With that ammo having a spread that big in that range, it must not have a big detrimental effect on accuracy.

Most long range competitors seat bullets in case necks sized to give about a 10 to 15 pound release force; that's enough to protect them in normal handling. Even with a 1/2 thousandth spread in neck wall thickness, the release force spread's gonna be no more than a few pounds.

Therefore, I'd put your neck tension concerns near bottom of your list of accurate ammo priorities. There's a greater spread in velocity caused by primer's spread in energy/heat release across a lot of them as well as the energy in exact charge weights of powder.

 

[MontanaRifleman]

cerwin, I think what you are referring to as a case holder is actually a shell holder? What you place on the ram to hold the case as you work it in press.

Yes i realize what you were using the Sinclair expander die for... I googled it and found a youtube video that demonstrated it. I like it and will probably adapt it. I'm also learning.

That said, if you have any irregularities in your neck, they will be moved back inward when you Neck or FL size your brass without an expander ball. Not sure how that affects neck tension?

Bart, I do realize that seating the bullet will move those irregularities back out, but my question is, is consistency of neck tension affected? If an expander ball is used to move the irregularities outward, then you have a circular neck ring on the inside without irregularities to receive the bullets. it seems to me there would be more consistent neck tension with that scenario?

Not sure how much it matters and it may be one of those things I experiment with to see if there is a noticible difference. I should buy something cheap like a 308 to do my experimenting with

 

[Tidesloe]

Good question.

Military match ammo (M118 and M852 7.62 NATO stuff as well as M72 .30-06) has a release force (neck tension, in MIL SPEC terms) of at least 40 pounds. Some of the stuff I've measured has a 10 to 15 pound spread above that. But it still shoots 7 inches at 600 yards with bullets not as good as Sierra's match bullets. With that ammo having a spread that big in that range, it must not have a big detrimental effect on accuracy.

Most long range competitors seat bullets in case necks sized to give about a 10 to 15 pound release force; that's enough to protect them in normal handling. Even with a 1/2 thousandth spread in neck wall thickness, the release force spread's gonna be no more than a few pounds.

Therefore, I'd put your neck tension concerns near bottom of your list of accurate ammo priorities. There's a greater spread in velocity caused by primer's spread in energy/heat release across a lot of them as well as the energy in exact charge weights of powder.

Well said, that seems to make sense to me. I do realize some of the things I may seem to prioritize may be negligible in the end, but part of my learning process, and attempts to eliminate any variable that I can. There are more important things to focus on, as youve stated above.
As far as the primer spread/release of energy. I've not done enough loading yet to see those variances first hand. I haven't chrono'd anything yet either. I suppose that is a necessary part of the process. What strategies are used to manage the effects of that variable?
I am trying to be very meticulously precise in my powder weights. I'm currently using RCBS's entry level balance beam scale, and that may produce some inconsistencies. For now, I'll have to make do with what I've got, and look for ways to manage any variables I see there.
It seems to me that the chrono is a must do thing. Heres a question about chrono. Will conditions that put the sun at the target end of the range have a negative effect on chrono accuracy? DST will help to an extent, but that is typically the conditions I'm shooting in, regardless of time of day.
Thanks for the input Bart

 

[Tidesloe]

cerwin, I think what you are referring to as a case holder is actually a shell holder? What you place on the ram to hold the case as you work it in press.

Yes i realize what you were using the Sinclair expander die for... I googled it and found a youtube video that demonstrated it. I like it and will probably adapt it. I'm also learning.

That said, if you have any irregularities in your neck, they will be moved back inward when you Neck or FL size your brass without an expander ball. Not sure how that affects neck tension?

Bart, I do realize that seating the bullet will move those irregularities back out, but my question is, is consistency of neck tension affected? If an expander ball is used to move the irregularities outward, then you have a circular neck ring on the inside without irregularities to receive the bullets. it seems to me there would be more consistent neck tension with that scenario?

Not sure how much it matters and it may be one of those things I experiment with to see if there is a noticible difference. I should buy something cheap like a 308 to do my experimenting with

Your right Rifleman, shell holder. We're not done here yet if you guy's are gonna get me up to speed. Bart seems to have a wealth of knowledge, and so do you. I read on here justifiable, reasonable defenses for one end of the spectrum to the other in nearly every aspect of the loading process. I at times become more confused after being on this site. More questions than answers, but thats a good thing. Questions lead to more questions, which in turn lead to more answers. In the end the answers I have to find for myself, but couldn't find any of them without all input, and knowledge from all you guy's. I think any dumb question is the one that isnt asked, and I'm full of dumb questions lol!!!

More to come fer sher!

 

[Bart B]

As far as the primer spread/release of energy. I've not done enough loading yet to see those variances first hand. I haven't chrono'd anything yet either. I suppose that is a necessary part of the process. What strategies are used to manage the effects of that variable?

It seems to me that the chrono is a must do thing. Heres a question about chrono. Will conditions that put the sun at the target end of the range have a negative effect on chrono accuracy? DST will help to an extent, but that is typically the conditions I'm shooting in, regardless of time of day.

Use Tulammo (formerly Wolf) primers from Russia. They're popular with long range competitors these days. And replace your firing pin spring with one10% to 15% stronger than the factory one. Primers need to be smacked hard to make them consistant. Those springs usually weaken over time and weak ones don't fire primers uniformly. Replace them every 2 or 3 years. Verify your firing pin protruded at least .055" from the bolt face but no more than .065"; not enough won't fire primers consistantly, either.

I've never owned nor used a chronograph working up a load. Just used loads that other folks got good results with. I did borrow one to see what vertical shot stringing there was at long range due to velocity spread and do some tests with ballistic software, but that's all. I think most chrono's have lights in their screens and the sun angle doesn't effect them. Check out the specs on some and find out for sure.

 

[Tidesloe]

Use Tulammo (formerly Wolf) primers from Russia. They're popular with long range competitors these days. And replace your firing pin spring with one10% to 15% stronger than the factory one. Primers need to be smacked hard to make them consistant. Those springs usually weaken over time and weak ones don't fire primers uniformly. Replace them every 2 or 3 years. Verify your firing pin protruded at least .055" from the bolt face but no more than .065"; not enough won't fire primers consistantly, either.

I've never owned nor used a chronograph working up a load. Just used loads that other folks got good results with. I did borrow one to see what vertical shot stringing there was at long range due to velocity spread and do some tests with ballistic software, but that's all. I think most chrono's have lights in their screens and the sun angle doesn't effect them. Check out the specs on some and find out for sure.

Bart, your a gold mine of knowledge and experience. I appreciate the info. I'll definitely be looking into the spring and pin protrusion thing.
Tulammo is components I never would have considered. I suppose some good stuff shows up in some unlikely places. Thanks for the tip