Pressure signs?

[bllistc]

Hey guys. I’m wondering if I’m loading this too hot but I’m not sure if I have pressure signs. Shooting an LMT308 with a 16” barrel

175gr SMK
44.7gr varget
Federal brass
CCI 200 primers
0.020” jump
Getting a mean velocity of about 2625 FPS

The first two pics there are some extractor marks on the rims. The last two the primers have a little bit of cratering. It’s not on all the cases and I can really only notice if I run my finger over the primer. Ive had a few blown primers but it was happening with lighter loads too so I’m thinking that’s just cus the primer pockets were loose. It’s 3x fired brass. Thoughts?

 

[spife7980]

It might be pressure issues... but being that its a semi auto it could also be premature extraction causing the symptoms. Not familiar with the LMT, any way to adjust the gas down at the gas block?

 

[bllistc]

It might be pressure issues... but being that its a semi auto it could also be premature extraction causing the symptoms. Not familiar with the LMT, any way to adjust the gas down at the gas block?

No it doesn’t have an adjustable gas block. Are there any other signs I would be seeing if it was premature extraction?

 

[spife7980]

I dont know but the ejector imprint and the bent rim from the extractor are what I noticed in mine and adjusting my gas block eliminated them.

 

[MarinePMI]

Listen to what Spife is saying...

 

[spife7980]

That said, 44.7 gr of varget isnt necessarily a not too hot load either.

You say it was blowing primers, what do you mean. Were they puncturing or were they actually blowing out and falling out of the primer pockets?
Do the ejector and extractor marks go away at the lower weight charges?

 

[bllistc]

That said, 44.7 gr of varget isnt necessarily a not too hot load either.

You say it was blowing primers, what do you mean. Were they puncturing or were they actually blowing out and falling out of the primer pockets?
Do the ejector and extractor marks go away at the lower weight charges?

Yea I know it’s pretty close to the max pressure. The primers were falling out of the pockets. No punctures. I just looked at box of factory Lapua brass I ran through it and didn’t have any extractor marks.

I’m gonna drop the charge by a a few grains and reload some rounds with fresh federal brass and look at that.

 

[spife7980]

OK, well that sounds about par for the course after 3 hard firings, federal brass is generally regarded as some of the softer brass you can get.

 

[PatMiles]

Put together a 6.5 CM AR-10 for my 12 year old granddaughter to hunt with. Initial shot with mild factory ammo showed the same symptoms as the OP's brass as well as longitudinal scratches on the brass. An adjustable gas block cured everything.

 

[bllistc]

Hmm. Ok so it looks like I’ll start looking into adjustable gas blocks as well. That’s really the only downside to this rifle is the lack of one. Thanks for the help fellas.

 

[Dolomite_Supafly]

I run an adjustable gas block on every AR I own. Very few guns are gassed correctly and most times they are over gassed. The reason is manufacturers do not want guns coming in for warranty work when they won’t fire cheap combloc ammunition so they drill the ports larger and the result is an over gassed gun.

A tuned gun will have less felt recoil, less gas in the face of the shooter, less crud in the receiver and it will be quieter to the shooter with a silencer because the port noise will be reduced.

I have a sub 6 pound AR I built that is perfectly gassed. Most people who shoot it think I am using special ammunition because it feels like a 22 long rifle.

 

[918v]

Yea I know it’s pretty close to the max pressure. The primers were falling out of the pockets. No punctures. I just looked at box of factory Lapua brass I ran through it and didn’t have any extractor marks.

I’m gonna drop the charge by a a few grains and reload some rounds with fresh federal brass and look at that.

You need to start understanding how case capacity affects pressure. The data you are relying on is based on high capacity Winchester brass and you loaded it in low capacity Federal brass and now your primers are falling out. You need to reduce that load by 1.5 grains.

 

[Doom]

I’ll probably regret posting this but based on your load, velocity, barrel length and the fact you’re in Federal brass you are likely over pressure on the cartridge and definately on the gas system. Hodgdon list 45gr in Winchester brass for a bolt gun and Sierra lists 43.8gr. Adjustable gas block will reduce the brass wear and tear from extraction. The velocity you are getting is more typical of a 22” or 24” barrel.

 

[Cascade Hemi]

I’ll probably regret posting this but based on your load, velocity, barrel length and the fact you’re in Federal brass you are likely over pressure on the cartridge and definately on the gas system. Hodgdon list 45gr in Winchester brass for a bolt gun and Sierra lists 43.8gr. Adjustable gas block will reduce the brass wear and tear from extraction. The velocity you are getting is more typical of a 22” or 24” barrel.

What Doom said. 175SMK going 2625fps out of a 16" barrel is blazing fast. Factory 175 FGMM runs around that speed out of a 22" to 24" bolt gun. I'd start by backing the load down to around 2500fps on the high end, and even that is probably higher pressure than I'd want in a gas gun.

 

[mudpig]

To echo CH.....I've got a 18" gas gun and 175 FGMM runs 2502fps from it.

 

[bllistc]

Damn. Ok I didn’t think of that. I just got the magnetospeed recently and haven’t chrono’d factory Ammo. I knew I was loading it hot but didn’t realize it could be that high.

I’ll go back and re-check but I think the node I had was 43-45gr. So I’m thinking I’ll go back to 43.2-43.5gr and chronograph that. Or should I just run a ladder test from 43-44gr going up by 0.2gr increments?

 

[Tchitcherine]

If there's any doubt about loose primer pockets in the brass you are reloading, these go/no-go gauges are useful: https://ballistictools.com/store/small-and-large-primer-pocket-gauges

ETA: Not suggesting that is the cause of your problem. It could be an effect of your problem from firing hot Loads.

 

[Cascade Hemi]

Damn. Ok I didn’t think of that. I just got the magnetospeed recently and haven’t chrono’d factory Ammo. I knew I was loading it hot but didn’t realize it could be that high.

I’ll go back and re-check but I think the node I had was 43-45gr. So I’m thinking I’ll go back to 43.2-43.5gr and chronograph that. Or should I just run a ladder test from 43-44gr going up by 0.2gr increments?

Do you like buying new brass after each firing? Start at 41gr and work up to around 2450fps. 44gr of Varget in FC cases is still almost 60k PSI.

 

[Doom]

With Federal brass you shoud find nodes around 42gr and 43.2gr. The 43.2 node may be too hot depending on your rifle. The 42 gr load should approximate the FGMM 175 load.

 

[bllistc]

Right noted. I’ll start back down at 41gr