As the title states i have a 375 RUM that i built to do some long-range elk hunting with. Long story short I did a load workup and everything was great for a little while but i started running into random pressure signs and my groups opened from .5 to about 1.5 inches. I did a workup with Bertram brass, cci 250, magpro powder, and a 350 cutting edge MTH. When I say I hit random pressure signs I can shoot a round and it will be fine, but the next one might have a little bit of a sticky bolt lift and an ejector mark. Then my next round is back to normal. After the workup i shot about 40 rounds with it being consistent. I ended up checking OAL and they're all within 1 thousandth of each other. So I weighed my Bertram brass and I had a 12 grain extreme spread with about an 8 grain average. Is this enough to cause what I'm seeing or should I be looking elsewhere? Thanks
375 Rum inconsistent pressure signs
- Thread starter chrisb97
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Calvin45
Well-Known Member
What powder you running and approx what % case fill? are the bullets jammed into the lands or being allowed to jump a ways or somewhere in between? And what do the primers look like on the "fine" rounds…are they pancake flat and cratering?
I've found a little jump or freebore dampens out a loads susceptibility to spiky pressure variations. And with big magnums a 100 percent case fill of appropriate burn rate powder is always a good thing.
8 grains average variation in brass weight on a case that big won't single handedly make this kind of difference.
Im running Magpro powder at 97.1 grains but im not sure of the fill ratio. And there's no flattening of the primer even on the rounds that exhibited the other pressure signs. I used cutting edges recommended seating depth because of the seal tite bore rider and it is just barely touching the lands. The chamber was cut for me to have a little bit of freebore for the 350 smk but i had to switch to the MTH as i just cant find any matchkings.
Calvin45
Well-Known Member
Hmmmm
What is your chronograph telling you? Are the shots that result in sticky bolts and ejector marks going faster?
Is all the brass the same regarding number of firings? Subsequent firings don't matter as much but there can be a real difference between virgin and previously fired brass. Are some of the cases in these loads virgin and some not?
Finally, and this may seem silly but not a bad idea…have you checked the accuracy and consistency of your powder scale against another scale as a control? Cuz that'd do it, especially if you're using an electric scale and it's on the fritz
What is your chronograph telling you? Are the shots that result in sticky bolts and ejector marks going faster?
Is all the brass the same regarding number of firings? Subsequent firings don't matter as much but there can be a real difference between virgin and previously fired brass. Are some of the cases in these loads virgin and some not?
Finally, and this may seem silly but not a bad idea…have you checked the accuracy and consistency of your powder scale against another scale as a control? Cuz that'd do it, especially if you're using an electric scale and it's on the fritz
memtb
Well-Known Member
I may be way off with this…..but is it possible that the brass my be touching/jamming the end of the chamber or you may have a bit of a carbon buildup and the case is jamming into it! Just a wide guess…..grabbing at those straws! memtb
I just checked my OAL and i must have messed something up Because i have over .200 freebore. I dont believe so on the carbon or jamming because the same range day i threw some factory remington ammo in it and stacked them on top of each other and the remington brass is a few thousandths longer than my bertram brass. My chronograph says theyre not too far off from each other and the cases are on their third firing. When i measure my powder I use a chargemaster set to .1 under than transfer to a beam scale and trickle the last tenth in.
Calvin45
Well-Known Member
Right on.
Odd all around for sure but I'm sure there's a reasonable explanation.
You said the Remington factory ammo didn't do this right?
Do you happen to have any other handloads to check this against? If none of your handloads with other components are doing this then that's an easy button: there's something inconsistent about the powder, the projectiles, or even the primers (but that's not very likely).
If other handloads are doing this and factory isn't there's something funny going on here indeed.
Finally, and I can't believe I'm even saying this as I'm such a skeptic of the idea in general, but is there a chance there's some kind of cold welding happening between bullet and case neck? I ask because you say that everything was fine a while ago and now it's doing this. Does that mean you're still working with the same batch of ammo you did up a while ago which was fine then and isn't now? If so, how long ago and do you live in a humid climate? Or do you mean this load recipe used to be great and now when you recreate it this happens? If so…same lot of powder?
Odd all around for sure but I'm sure there's a reasonable explanation.
You said the Remington factory ammo didn't do this right?
Do you happen to have any other handloads to check this against? If none of your handloads with other components are doing this then that's an easy button: there's something inconsistent about the powder, the projectiles, or even the primers (but that's not very likely).
If other handloads are doing this and factory isn't there's something funny going on here indeed.
Finally, and I can't believe I'm even saying this as I'm such a skeptic of the idea in general, but is there a chance there's some kind of cold welding happening between bullet and case neck? I ask because you say that everything was fine a while ago and now it's doing this. Does that mean you're still working with the same batch of ammo you did up a while ago which was fine then and isn't now? If so, how long ago and do you live in a humid climate? Or do you mean this load recipe used to be great and now when you recreate it this happens? If so…same lot of powder?
Yeah remington factory 300 grain shot within .75 inches and my handloads during workup shot just under half for a group of 5. All of these handloads were loaded in the last 2 months and I live in Southern Oregon so it's not very humid here. And yeah this load used to be great but recreating it is giving some not great results. I do believe my powder is different lots as I only have 1 pound containers
MagnumManiac
Well-Known Member
Very first thing I would check is CBTO on these rounds in comparison to older rounds or notes you have taken. If different then this could account for the issue because the load may have dropped out of a node at that measurement.
I had fits with my 338 Edge, as the barrel sped up, so did pressure and it would go on wild excursions for no apparent reason. In the end, I had to re-chamber the barrel, do away with the turn neck dimension and add +P throating. Pressure excursions stopped after this, but I still wasn't happy and sold it.
It could also be a powder issue, which I wouldn't disregard, some lots are very different to each other.
Cheers.
I had fits with my 338 Edge, as the barrel sped up, so did pressure and it would go on wild excursions for no apparent reason. In the end, I had to re-chamber the barrel, do away with the turn neck dimension and add +P throating. Pressure excursions stopped after this, but I still wasn't happy and sold it.
It could also be a powder issue, which I wouldn't disregard, some lots are very different to each other.
Cheers.
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What is your BTO and COAL?
COAL is 4.257" and the projectile is too long to use a comparator. Being a lathe turned solid they are very consistent so i have just been going off OAL. This chamber was cut for the 350 sierra matchking which has the ogive much more towards the tip of the bullet compared to the cutting edge. I am starting to wonder if i just have too much freebore. The only thing that stumps me about that is these bullets used to shoot good out of this. I have about 150 rounds down the tube now.
Buy a Sinclair comparator body, they are easily long enough to allow you to measure the super long solid bullets
What bullet seating die are you using?
The Cutting Edge bullets I've shot have a seal-tite band, and the seal-tite band contacts the entrance to the throat before the ogive contacts the lands.
Cutting Edge recommends seating their bullets into the case neck such that the seal-tite band is located 0.005", or 0.020-0.025", off the chamber throat. Which places the seal-tite band very close to the case mouth.
In post #3, you stated your bullets were seated with the seal-tite band barely touching the lands. Did you mean the lands, or did you mean barely touching your chamber throat?
Because the distance from the bullet ogive to the lands with the Cutting Edge bore rider style bullets isn't used to determine the recommended bullet seating depths. The recommended bullet seating depth is a distance specified from the seal-tite band to the chamber throat. Which means the seal-tite band is normally almost touching the mouth of the casings.
Cutting Edge recommends seating their bullets into the case neck such that the seal-tite band is located 0.005", or 0.020-0.025", off the chamber throat. Which places the seal-tite band very close to the case mouth.
In post #3, you stated your bullets were seated with the seal-tite band barely touching the lands. Did you mean the lands, or did you mean barely touching your chamber throat?
Because the distance from the bullet ogive to the lands with the Cutting Edge bore rider style bullets isn't used to determine the recommended bullet seating depths. The recommended bullet seating depth is a distance specified from the seal-tite band to the chamber throat. Which means the seal-tite band is normally almost touching the mouth of the casings.
