rafsob

Is anyone else having pressure problems loading for their AR or gas guns for the 7.62/.308??

I loaded some test loads for my new DPMS GII hunter 7.62 AR . Well had no problem with CFE 223 powder, but had a lot of problems with IMR 4895!!! My Hogden book had load data for the .308 at 42.7 to 45.5c.

Well I ended up blowing out the primers on all the IMR 4895 bullets I loaded.

Sorry for the blur, but here you can see the two extractor marks in the base and they impacted really hard:



After finding an article from the annual Hogden reloading book 2014 manual, I found I was over loading this round for this type of gun. Don't know why this powder company doesn't give this info out in their book is beyond me.

I have been reloading over 50 years and feel like a rookie on this matter. It makes me mad to think I could have one been hurt or blown my rifle up!!!

Here is a photo of my test loads. On the right was my CFE223 loads, no problem. the ones on the left were the IMR4895 loads. Everyone I fired had a blown primer. I loaded starting with 43 grs to 44.5 grs. Just glad I didn't start at the 43.5 rounds!!!!!



Being this is the first time I am reloading for a gas gun, I wondering it the gun has a problem or I need to stick with commercial rounds. I could do this because I plan to hunt with this gun. Any ideas or recommendations guys?

Tufrthnails

I load .223 for my AR. I havn't run into the issue myself, but have heard of guys having problems with data before. So what I do is load a grain or two below single rounds moving up .2 increments until the rifle will cycle to the next round and stop at that point and start my normal load development ladder there 5 rounds at a time.

rafsob

Sounds like this is what I will have to do also. Just bothers me that the Hogden company doesn't recognize this problem even after they put an article in their own magazine that identifies this vey problem!!! They aren't the only company that publishes reload manuals, Speer, Harnady, and Sierra to name a few.

rafsob

I check the DPMS website and they have a disclaimer:

Ammunitions Warning

After extensive testing, we have found that only ammunition manufactured to SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specifications is reliable in DPMS rifles. DPMS recommends the use of high quality, domestically produced ammunition for best results and highest accuracy. For plinking and practice, we recommend only domestic, commercially manufactured ammunition. Please note: the use of hand-loaded ammunition voids the factory warranty. The use of all ammunition listed below also voids the warranty.
We have incurred feeding problems with the following:
Israeli ammunition
Korean ammunition
Chilean ammunition
Portuguese ammunition
We have reviewed several reports, from several manufacturers', regarding problems using this ammunition. The problem appears to be the bullet contour and the overall length of the cartridge, which is contacting the rifling before firing. This is creating a gas port pressure and chamber pressure higher than recommended, therefore causing feeding and extraction problems due to the increased bolt carrier velocity. In addition, there is accelerated fatigue on internal parts. There are also indications that brass may be out of spec, which could create an unsafe condition.
PMP
South African produced surplus
We have used this ammunition in the past for testing purposes and found the brass is extremely soft and can "flow" into microscopic pores and grooves in the chamber creating "sticky" extraction. This has been reported in many types of rifles, but is more prevalent in semi-automatic weapons.
Lacquer Coated Ammunition or Steel-cased, lacquer coated ammunition
Wolf
Norinco
Silver Bear
Any steel-cased (coated or non-coated) ammunition
The problem with this ammunition is that the lacquer coating on the case. As the barrel heats up, the lacquer turns to a soft, varnish substance and upon cool down, becomes very solid and difficult to remove. This effectively creates an undersized chamber and creates understandable problems.
Your rifle is an investment and it only makes sense to choose quality ammunition for a quality rifle!

So I don't think I'll get much help there. I plan on buying some commercial ammo and see if I get the same result as my reloads. Will get back to the forum on what I get. Sure hop I don't have a gas pressure problem in this gun!

Ridge Runner

tear your bolt down and clean it before it gives you trouble. not sure what the deal is there about pressure problems unless your rifle is chambered 7.62x51 instead of 308, saami specs state a lower max pressure for the 7.62.
RR

Nomercy448

This can be a sign of over-gassing, as well as a sign of over pressure rounds. The bolt is retracting before the chamber pressure dropped sufficiently to be safe for your particular load.

This problem tends to rear its ugly head more predominantly in the AR-10/LR-308 platforms than it does in AR-15's, but the same problem is common for both in current production models.

Most current production factory models are significantly over-gassed by design to ensure reliable function. They beat the he11 out of brass, but they'll cycle almost anything you feed it.

There are several fairly common band-aid fixes, and one proper fix.

Proper Fix - spend the money and buy an adjustable gas block.

Band aid 1 - crimp the gas tube to limit flow. Inexact science, but it works.
Band aid 2 - loosen the gas block and turn it slightly out of alignment over the gas port.
Band aid 3 - run lighter loads to reduce the gross pressure. Sucks sacrificing power though.
Band aid 4 - heavier buffer or bolt carrier and stiffer spring. Slows the opening, but doesn't really fix the true problem.

Personally, I'd throw on an adjustable gas block, work up my loads with it, and be happy. (Which is what I do for all of my AR platform rifles).

super_hunt54

Since I use a can (suppressor) sometimes on my AR's I have AGB's on all of them. Never ran across this problem with mine but I would suspect Mercy's correct in his assessment. I load some pretty stout loads in both my 7mm-08 and my new .338fed AR's and have no pressure problems from either of them. AGB's aren't all that expensive and are great for that refined tune that some of us like to get for ultimate performance from our rifles.

Tufrthnails

I didn't think of that I only run AGBs.

rafsob

Thanks for the input Mercy. Don't know if this has any effect on my problem, but this GII is unique in that the receiver is really an AR-15 platform shooting a .308 round. The gun itself is very light compared to an AR-10 gun.

Before I do anything else, I plan to buy some off the shelf ammo and see if that has any problems. I may have a gun problem! I guess my biggest complaint is the difference in loads for the IMR4895! My research on this powder shows I should not be going over 41grs vs what the reload books call for - 42.7 to 45.5c. I'm thinking that the receiver could have blow up!!!

I know almost all gun manufacturers call for only commercial ammo should be used in their guns, but reality shows that we normally like to reload for our guns. I would hate to see someone getting hurt by following these reload books in the case!!!!!

Nomercy448

Case head swipe (your extreme ejector marks and the swipe marks with them) and blown primers are really only signs of over gassed actions. Over-gassing CAN be caused by over-pressure rounds, in which case if you closed your gas block, you'd see cratered primers and other common pressure signs (closed gas block almost always causes sticky extraction in AR's, so that's not a good indicator). BUT these signs aren't necessarily a sure fire indicator of over pressure.

Case head swipe and blown primers are caused by the action opening while the chamber pressure is still very high - the case head is still pressed hard against the bolt face while the operating gas is trying to turn, "swiping" the case head. Of course, this means the primer is no longer supported as the bolt moves, and it's free to blast out of the tail of the case. If the over gassing is caused by over pressure rounds, if you throttled down the gas flow, you'd still see normal over-pressure signs similar to any other action. If it's simply caused by over gassing, the brass would look fine after throttling down. You'll also see substantial extractor and ejector impressions, not just swipe marks.

Since you do look to have pretty substantial impressions, not just swipes, your load probably really is over-pressure - but it's hard to tell in the pics.