Pressure spikes with varget?????? Please help

[StockDog]

I have been working up some loads for my 18" ar10, noveske barrel.
The extractor is raising a bur on the face of the case.

It is happenning at an increasing rate as I get above 43 grains.

Here is my load.
175 smk
42.5, 43
Cci lr primes
fc cases

it is also happenning with this load and workup
155 amax
42.5. Good
43. 1 of 5 cases
43.5. No marks
44.0. Light marks or peels
44.5 3 of 5 rounds

I did not get pressure signs with this load. It should be a hotter load.
175 smk
43.0. Rl15
43.3 rl15
fc cci primers
I tried the search function and came up with pages of varget info. Most all of it was just talking about what people are using.

I am following the manual information from the mAnufacturer and crosseferencing it with my other manuals.


155 amax

 

[mavrick10_2000]

Re: Pressure spikes with varget?????? Please help

How far are you seating the bullets out of the lands? This is my first guess.

Is this new/once fired FC Brass? What's your case length?

For a bolt gun you are at really light loads. For a gasser those loads on the 155's might be in a pretty good range for your AR10. The issue is every rifle is different.

I'm not seeing any Chrono data, so I'm assuming you don't have any speed data to provide another set of details.

 

[StockDog]

Re: Pressure spikes with varget?????? Please help

All smk bullets seated at 2.805 coal. I am then measuring them to the ogive for consistency.

The cases are on their 3rd firing.

I also swapped bolt groups and it still happenned.

I am running an MGI heavy buffer with spacer for a full length stock. I have confirmed that it is the correct one.

The 43.5 and 44 grain load were both giving me half inch groups.

I cam switch to lc cases and back the powder charge down. If so how much?

Primers looked normal. They still had the bevel visible around the edge.

I don't have a chrono.

I was wondering if I got a hot batch of varget?

 

[Dreamweaver]

Re: Pressure spikes with varget?????? Please help

Difficult to say without a chrono.

My standard 175 SMK load is 42.2 of Varget in my DPMS 16" but this is only 2,420 fps which i find to be the low speed node.

The high speed node was 45.0 which was 2,500 fps which is approaching the max for a 16" barrel and a 175 SMK but this had too many pressure signs, flat primers, couple of blown primers, hard extraction marks.

I'm using WIN brass...i did read somewhere that mil brass has a lesser volume than factory brass but i have no idea if this is right or the effect range it would have.

Just some thoughts...

~Mike

 

[StockDog]

Re: Pressure spikes with varget?????? Please help

42.5 varget is the tightest grouping so far. I'll just shoot it at some distance and compare to my balistic program and get in the ballpark for FPS.

I have cleaned the barrel and chamber. Lubed the bolt group well. I'll just back it down some and shoot. I may also try the 155 amax with RL 15.

If you are getting 2420 in a 16" at 42.2 hopefully I can hit 2500 with 42.5 in my 18".

 

[Fuzzball]

Re: Pressure spikes with varget?????? Please help

Not only do rifles/chambers vary, so does the alloy in the brass. If we have a soft spot in a case we get real "pressure" signs but it may only apply to that case.

 

[cmh2007]

Re: Pressure spikes with varget?????? Please help

i had 3 flattened primers out of 100 with almost that exact 155 gr load, except mine was in cbc cases with 44.5 gr of varget

 

[308sako]

Re: Pressure spikes with varget?????? Please help

Deleted in protest!

 

[StockDog]

Re: Pressure spikes with varget?????? Please help

I will checkout the headspace techniques.

I set my dies off of the chamber in my 5r. I chamber brass that is very tight or the bolt will not close on. I then progressively adjust the die until the bolt will close with light pressure. I assume that the chamber on my 5r is tighter to saamii spec and the ar10 chamber has a little more tolerance. It is a noveske 18" barrel that is supposed to be cut for m118lr specs.

I'll also look into buying a chrono.

 

[Greg Langelius *]

Re: Pressure spikes with varget?????? Please help

Those Varget loads, by themselves, should not be generating spikes. and your OAL's seem conservative.

I would suggest that the chamber/throat of the custom barrel may be on the tight side, allowing some cases to spike and others not, without any outward differences being apparent. Mic'ing the neck thicknesses on the affected cases may lend some light to this problem.

Meanwhile, temporarily cull the cases with pressure signs, and see if his affects the outcome.

Problems like this are a prime reason behind my decision to stick with SAAMI chamber specs.

Greg

 

[ArcticLight]

Re: Pressure spikes with varget?????? Please help

2.805 - factory is 2.810 I believe.

First thing I'd do is get rid of the FC brass and try some Winchester - change nothing else.


Then try some Federal primers. I've heard from a lot of people that CCI's tend to go a lil hotter than Federals.

Federal Brass - blah, but Federal Primers - yeah..

Just MHO

 

[sharpshtr66]

Re: Pressure spikes with varget?????? Please help

can you post pics of the cases showing whats going on, and what is your gas system length?

 

[StockDog]

Re: Pressure spikes with varget?????? Please help

the right side 20 were 42.5 var cci lr primer fc cases
you will see 1 win case slipped in there


Extractor peel

necks a little sooty

closeup

cases as seen L to Rt ( 2 peels are at 42.5 varget)
155 amax cci primers fc cases 4x loaded
45.0 (unfired) ,44.0, 43.5 43.0 42.5. As seen in picture

the 2 pee

 

[MitchAlsup]

Re: Pressure spikes with varget?????? Please help

I see one primer pocket that is leaking but otherwise no pressure signs on the primers--not cratered, not flattened, nice rounded edges.

I think those cases need a good overnight run in the tumbler.

 

[sharpshtr66]

Re: Pressure spikes with varget?????? Please help

It looks just like the ejector is scraping from the bolt unlocking early, are any of the rims bent from the extractor? or deep extractor marks? if so the bolt is trying to extract the shell before chamber presure has droped sufficiently. very common with carbine length gas systems, I had a similar problem, adjustable gas block took care of it.

 

[StockDog]

Re: Pressure spikes with varget?????? Please help

It has. Mfi buffer and spacer in it. I qil swap it for a standard rifle buffer and see if this fixes it. I'll try the gas block next.

It is a mid length gas block.

 

[308sako]

Re: Pressure spikes with varget?????? Please help

Greg makes a very good point about the chamber maybe being a little short. Also the culling of the pressure sensitive cases wouldn't be a bad place to start either.

Way to go Greg.