Why would the starting load back my primers out?

shmelmafinga

shmelmafinga

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My first try at loading 60gr Hornady Vmax for my XCR:

CCI 450 primers, Remington brass, full length resized, trimmed to 1.75", COAL 2.26".

Started at 25.0 grains of Varget and moved up to 26.5 grain compressed loads of five rounds each.

The first five rounds were the most accurate, but the spent cases all had their primers backed out slightly. (1" group)

In increments of 0.5 grains I increased the powder charge. Everything higher than 25 grains had no problem signs, but had drastically worse accuracy. (2" groups and worse)

Why would the lightest load back my primers out, yet be the only decently accurate load of the bunch?
 
This light starting load backs out your primers because there is insufficient pressure to fully obturate the case. The firing pin drives the case forward as far as it can go into the chamber, the pressure builds sufficiently to cause the case walls to adhere to the chamber walls, but there is not enough pressure to stretch the case slightly so the case does not back right up to the boltface. However, the pressure pushes the primer out till it touches the boltface, leaving it slighlt protruding from the case. As pressures increase, the case is forced back against the boltface, and the problem disappears. As for accuracy, you should be able to find another "node" of good accuracy closer to max pressures somewhere. Work up carefully in .5 grain increments. The accuracy should improve somewhere during this process. Regards, Eagleye.
 
When you seat the primers do they go in there snug or loose?

"VTR in 223 shoots best .005 off the riflings,best group to date .365 with 60 grain v-max and H335 powder."

I was trying to find some information at what velocity the 60 grain bullet performs best at but I am having a hard time finding it.
 
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Eagleye explained it well.

He is a very experienced hand-loader with years of practical knowledge and you would do well to listen to his advice.
 
I had a P-17 30-06,now a 308Norma,with headspace questions;).Like about 12 of them,6 is enough.I got primers protruding. By measing cases before and after with the primer,I got the headspace number,I used a guage later to check.It's not the recommended way,but if primer sticks out,measure.
 
shmelmafinga said:
My first try at loading 60gr Hornady Vmax for my XCR:

CCI 450 primers, Remington brass, full length resized, trimmed to 1.75", COAL 2.26".

Started at 25.0 grains of Varget and moved up to 26.5 grain compressed loads of five rounds each.

The first five rounds were the most accurate, but the spent cases all had their primers backed out slightly. (1" group)

In increments of 0.5 grains I increased the powder charge. Everything higher than 25 grains had no problem signs, but had drastically worse accuracy. (2" groups and worse)

Why would the lightest load back my primers out, yet be the only decently accurate load of the bunch?
Click to expand...

Remington Brass is marginal at best and the primer pockets are Sh!t - your load is likely good.
The higher loads are likely not doing much but raising pressures, and 26.5 grains at that oal is already too much.
 
I exclusivly use remington .223 brass I have loaded everything from from min to max and a experimented with handgun powders and subsonic... I have never had any problems with the brass or primers backing out... I am pretty sure eagleye might be on to something but I cant see how under the recoil and pressure even if the headspace is wrong that the brass would not be pressed up against the bolt face all the time durning the igintion of the powder...
 
Eagleye said:
This light starting load backs out your primers because there is insufficient pressure to fully obturate the case. The firing pin drives the case forward as far as it can go into the chamber, the pressure builds sufficiently to cause the case walls to adhere to the chamber walls, but there is not enough pressure to stretch the case slightly so the case does not back right up to the boltface. However, the pressure pushes the primer out till it touches the boltface, leaving it slighlt protruding from the case. As pressures increase, the case is forced back against the boltface, and the problem disappears. As for accuracy, you should be able to find another "node" of good accuracy closer to max pressures somewhere. Work up carefully in .5 grain increments. The accuracy should improve somewhere during this process. Regards, Eagleye.
Click to expand...

Exactly.:)
 
Like everyone else here, I am still learning. I only started reloading in 1966, so I am sure that there are plenty of things that I still can find out. But this matter of primers backing out with light loads [even with a perfect length (headspaced) chamber] is a phenomenon I have seen and experienced many times over the years. It is particularly noticeable in rimless or rebated case designs. Two commonly seen signs of very low pressures are slightly backed out primers and cases that are smoked up on the outside of their body. As pressures rise to normal levels, these irregularities also vanish.
This is precisely why, if one sizes his brass a bit too short for his chamber, the cases will separate just above the web of the case. When the firing pin drives the case as far forward in the chamber as it can, and then the rising pressure causes the case walls to adhere to the chamber, the head of the case is unsupported by the boltface. Continuing pressure rise now forces the head of the case back into contact with the boltface, stretching the case just above the head. It does not take very many repeats of this to produce a separated case, sometimes as soon as the 2nd or 3rd firing. Obviously, excess headspace will produce similar results, but that is quite uncommon in a modern rifle produced today. If I end up with a low pressure starting load that shows primer protrusion in a known good firearm, that particular piece of brass goes straight into the brass discard bin, since it has already been subjected to conditions that will precipitate a head separation in subsequent firings. Regards, Eagleye.
 
Yeah, okay. I think I get it. No flattened primers or anything to indicate overpressure, but the cases with the backed-out primers definitely are blacker on the outside than the others.

Thanks for the advice. I'm a little nervous about this XCR. It's really a piece of junk you know, but I paid my money and need to make it shoot now.
 
XCR.. like this?
ra_XCR_Brochure_2.jpg
 
I shoot mostly reduced loads in many diff. calibers, and am always experimenting. I shoot the .300 Whisper down to 500fps or so, the .308 down to 1200fps. I test cast bullets at speeds as low as I dare go and as high as i dare go, and i do not get primers backing out of cases on firing. There may be 2 reasons for this, I think the case matches the chamber very well, at least that's what I strive for, and the bullets are always seated well into the rifling, making it difficult for the case to be moved by the strike of the firing pin.
 
This light starting load backs out your primers because there is insufficient pressure to fully obturate the case. The firing pin drives the case forward as far as it can go into the chamber, the pressure builds sufficiently to cause the case walls to adhere to the chamber walls, but there is not enough pressure to stretch the case slightly so the case does not back right up to the boltface. However, the pressure pushes the primer out till it touches the boltface, leaving it slighlt protruding from the case. As pressures increase, the case is forced back against the boltface, and the problem disappears. As for accuracy, you should be able to find another "node" of good accuracy closer to max pressures somewhere. Work up carefully in .5 grain increments. The accuracy should improve somewhere during this process. Regards, Eagleye.

X2 Eagleye knows what he is talking about, I've had it happen myself.
 
ben hunchak said:
I shoot mostly reduced loads in many diff. calibers, and am always experimenting. I shoot the .300 Whisper down to 500fps or so, the .308 down to 1200fps. I test cast bullets at speeds as low as I dare go and as high as i dare go, and i do not get primers backing out of cases on firing. There may be 2 reasons for this, I think the case matches the chamber very well, at least that's what I strive for, and the bullets are always seated well into the rifling, making it difficult for the case to be moved by the strike of the firing pin.
Click to expand...
I'm sure you're right, but under most conditions, Eagleye has the answer.
I've been reloading since the '70's. I've had backed out primers from mild loads, even blackened cases, from the same cause.
Back to the original post
You can try neck sizing, or partial full length sizing your cases, if you want to use lighter loads. This accomplishes much of what Ben is saying above. It may improve the accuracy problem as well as help with the primers.
 
msg.drew said:
I exclusivly use remington .223 brass I have loaded everything from from min to max and a experimented with handgun powders and subsonic... I have never had any problems with the brass or primers backing out...
Click to expand...

Remington brass is well known for having excessively loose primer pockets when used in autos after as little as once re-loaded. Having primers pop out into the fire mech. sucks -speaking from experience.
I'm not sure why, but it seems to me there are quite a few on this board that believe what works in a bolt gun automatically works in an auto. I'm not saying that is the case here, but those who load for autos should be advised of this.

msg.drew said:
I am pretty sure eagleye might be on to something
Click to expand...

Without doubt.
I pointed out the brass as this is an obvious issue for anyone who has time loading for an auto...as always, ymmv.

'shmelmafinga' - good luck with the XCR, I hear they rock!:cheers:
 
I have shot the same remington brass for the last 6-8 years in both bolt and Ar's with out any problems.

I have even used low velocity pistol powder loads in my ar without the primers backing out this exact load
55 GR. HDY FMJ Hodgdon Titegroup .224" 2.200" 3.1 1064 4,000 CUP
 
ben hunchak said:
I shoot mostly reduced loads in many diff. calibers, and am always experimenting. I shoot the .300 Whisper down to 500fps or so, the .308 down to 1200fps. I test cast bullets at speeds as low as I dare go and as high as i dare go, and i do not get primers backing out of cases on firing. There may be 2 reasons for this, I think the case matches the chamber very well, at least that's what I strive for, and the bullets are always seated well into the rifling, making it difficult for the case to be moved by the strike of the firing pin.
Click to expand...

Ben; You are exactly right in your deductions! If I am fireforming brass for some wildcats that are a bit of a problem because of odd length chambers, [my 30 Gibbs for example] I often seat a bullet right into the lands to prevent the case moving forward in the chamber from the firing pin strike. Once the case fully fills the chamber lengthwise, the primer protrusion cannot occur, unless you FL size and shorten the case again. Regards, Eagleye.
 
Eagle has it.

If you chamber a primed empty case neck sized case (no headspace issue) and fire it, you might see the primer power compress the shoulder and back the primer out.

it is a normal thing, work up to hotter loads.
 
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