300 RUM Issues...

[cohunter14]

I was shooting in 55 degree weather. Primers look fine, but no I haven't tried other primers. Have just used CCI 250 Mag primers. And I don't have access to a chronograph unfortunately. Might have to buy one sometime soon I guess...

 

[Deleted member 46119]

Yeah, as an example if I were getting 3,000 fps, I would need only 45 clicks at 700 and 71 clicks at 900, so there are some pretty big differences there.

Unless you've verified your FPS with a chronograph, I believe you are using a BC in your calculations that is too high.

I recommend you recheck your BC and chron numbers.

 

[cohunter14]

Unless you've verified your FPS with a chronograph, I believe you are using a BC in your calculations that is too high.

I recommend you recheck your BC and chron numbers.

I guess I just assumed with that many people shooting the 200gr accubond that the BC had been verified for the G7 Ballistic Program on this site. It gives a G1 BC of .588, which is also what Nosler gives out, and a G7 BC of .294. Could that information be that far off? I haven't ever heard anything about the BC's being off for this bullet.

 

[R.Morehouse]

There are differences. Not sure what the BC of the AccuBond is. But the Berger is .696 I believe with not a lot of bearing surface. My COAL is 3.843" and my friends is 3.9xx. Can't remember exactly. Every gun is different, and so is every barrel. How far off the lands are you? I am 50 thou off and my friend is 22 thou off.

I noticed you and your friend are running from 22 to 50 off. I am new to my RUM and reloading for it. Could you please tell me why so far off? I am not trying to be a wise guy I just was wondering if this is common for the round. I have been doing some load work using ( Sunday temp.55 in western pa. )91.5g Retumbo, Fed. 215, 208 A-Max seated just touching the lands, Ohler crono. doing 3100 with a standard deviation of 5fps. out of a 27.5" Shilen select match tube. Best 5 shot 300yd group 1.12". I don't know anything about seating so far out...I don't think this gun will do much better ( definitely not with me behind it ) than it is. But I have others that may benifit....gun)....Thank's for your input.

 

[BEEMAN]

With groups like that I would stop there to. I am 50 thou off with 91 gr H1000. I stopped there because it shot really good and didn't see the point of trying for another 50-100 fps. If I do my part it shoots some pretty nice groups. 1.25 three shot group at 400 yds last fall. When I started load development last fall we started as per Bergers instructions at 120 thou off and moved closer and mine tightened up at 50 thou off. We just re measured mine and my throat has eroded. So now I am actually 80 thou off the lands!! Time to rebarrel soon. I have around 1000 rds through it. If your gun likes that load and speed I think I would stop there. Be pretty hard to improve on that.

 

[D.Camilleri]

I honestly don't remember how far off the lands I am and don't really care, because it shoots very good at magazine length. Last I remember though is that I have a pretty long throat, so getting close to the lands isn't an option.

In regards to the low velocity with the OP rifle, I would take the gun to a smith and have the bore cast and measured. Sounds to me like a tight bore or possibly a rough bore that isn't fully broken in.

 

[cohunter14]

In regards to the low velocity with the OP rifle, I would take the gun to a smith and have the bore cast and measured. Sounds to me like a tight bore or possibly a rough bore that isn't fully broken in.

It is a newer gun with only 60 or so rounds down the tube. Can that cause an increase in pressure or decrease in velocity?

 

[mrultramag]

you really need a good chronograph to set out there at 15 ft to get your velocities. Prochrono is affordable and most people that own one like it. I love mine. Next, you need to determine if what your seeing is really an excessive pressure sign or not. I'm assuming your getting a half moon on the brass head from the ejector. Does the hole that the spring loaded ejector button sit on your bolt in have a burr or sharp edge or may not be perfectly flush? This can cause it to mark the brass probably well before top pressures are reached. How is bolt lift and ejection? you said primers look fine. In my experience with the ultra mags; you can definitely tell when you are pushing too hard because the primer pockets loosen significantly after the round is fired. You find this out when you are seating a new primer in your fired resized brass case. Maybe take a few of your fired brass and see how a new primer seats? food for thought.

 

[cohunter14]

Does the hole that the spring loaded ejector button sit on your bolt in have a burr or sharp edge or may not be perfectly flush? This can cause it to mark the brass probably well before top pressures are reached. How is bolt lift and ejection? you said primers look fine. In my experience with the ultra mags; you can definitely tell when you are pushing too hard because the primer pockets loosen significantly after the round is fired. You find this out when you are seating a new primer in your fired resized brass case. Maybe take a few of your fired brass and see how a new primer seats? food for thought.

I have not noticed any sharp edges, but I can check. I will also try to post a picture of the signs I have noticed on my brass. Bolt life and ejection have been fine. I have not reloaded any of my used brass yet, but I will also try to clean one up and put a primer in there to see if it seats correct. Thanks for the suggestions!

 

[cohunter14]

Here are some pictures of the pressure signs I noticed:

 

[mrultramag]

maybe I'm blind. I even blew up those pictures and I cannot see an ejector mark on that brass. usually the mark is well defined and when severe is quite a shiny mark. If primers seat well and feel decently tight (not ready to fall back out) and no other issues; I would progress with increasing the load if you want. Get a chronograph first so your not flying blind. I personally load 92 gr RL25 in Rem Brass, fed 215M primer, 200 gr Accubond, 3.65 OAL and get approx. 3150 fps. When I tried Retumbo I can't remember the exact charge but velocities were very similar but accuracy wasn't there in my gun. I think I went as high as 95 gr. Of course work up to those levels as each gun can be different in what load levels it will tolerate. Be safe.

 

[cohunter14]

I added some arrows to the spots that I have noticed:








The other thing I was thinking is even if I could increase this load by 2 grains, would that really jump my velocity up over 200+fps? I feel like I should be over 3,000fps and at 2,860 I am not sure that 2 grains would jump my up that much. Thanks for all the suggestions!

 

[BEEMAN]

Sorry if I missed it; but what kind of gun and action do you have? It doesn't look like over pressure to me. I also don't see any extractor marks. It looks like a circular mark or trimming of brass. Always hard to tell in pictures but that is what I see. Used to have a Winchester in 300 WSM that really shaved off brass.

 

[cohunter14]

It's a Remington 700.