Absolute Hunter pressure issues in 308

L

Legend

Member
Gun is a 16.5", 1-10 twist cut rifle barrel, 308 (bisley chamber). I've got a few good loads with the 137gr hammer hunters, and recently decided I wanted to try the 151gr absolute hunters for the added velocity of the design, yada, yada.

Problem is I am getting major pressure very early with the 151 gr AH bullets. For example, I get 2850 with the 137 hh loads. With the AH bullets, I start to pressure out at like 2550 (meanwhile, I can get 165 gr partitions to 2600). No clue why this is happening. I have now done full pressure tests with 8208 xbr, ar comp and varget. Getting pressure on everything at 2550 or even sooner, not even close to max published loads for similar bullets.

What could be causing this?

Thanks in advance
 
Are you jamming the AH hunter in the lands. Make sure you have a big enough jump. I now start my seating depth at 0.05" where as with cut and core bullets I started them at 0.02". These mono's do not like to be close to the lands and will create a huge pressure spike....like dangerous pressure spike!!! Check your seating depth and make sure you are not close to the lands.

I know this because I had the same problem with some HHT's in my 300 wsm.
 
Very true! Also remember that when you measure the ogive to base on Absolutes, there is NO ogive.
The first time the bullet reaches caliber diameter is at the shoulder of the bullet (first PDR band) near the nose.
Keep this in mind when you are trying to find your distance from the lands! You should make this jump significant (at least .020) or you will very likely run into premature pressure.
(This is one reason for the clarification warning for those about to load Absolutes for the first time.)
 
Legend said:
Gun is a 16.5", 1-10 twist cut rifle barrel, 308 (bisley chamber). I've got a few good loads with the 137gr hammer hunters, and recently decided I wanted to try the 151gr absolute hunters for the added velocity of the design, yada, yada.

Problem is I am getting major pressure very early with the 151 gr AH bullets. For example, I get 2850 with the 137 hh loads. With the AH bullets, I start to pressure out at like 2550 (meanwhile, I can get 165 gr partitions to 2600). No clue why this is happening. I have now done full pressure tests with 8208 xbr, ar comp and varget. Getting pressure on everything at 2550 or even sooner, not even close to max published loads for similar bullets.

What could be causing this?

Thanks in advance
Click to expand...
Legend,
Can you give us a bit more information on your load. Primers, powder charge, coal, brass, etc.
This will help us with a direction that can possibly lead to figuring out what is going on.
Thanks
 
Legend said:
Gun is a 16.5", 1-10 twist cut rifle barrel, 308 (bisley chamber). I've got a few good loads with the 137gr hammer hunters, and recently decided I wanted to try the 151gr absolute hunters for the added velocity of the design, yada, yada.

Problem is I am getting major pressure very early with the 151 gr AH bullets. For example, I get 2850 with the 137 hh loads. With the AH bullets, I start to pressure out at like 2550 (meanwhile, I can get 165 gr partitions to 2600). No clue why this is happening. I have now done full pressure tests with 8208 xbr, ar comp and varget. Getting pressure on everything at 2550 or even sooner, not even close to max published loads for similar bullets.

What could be causing this?

Thanks in advance
Click to expand...
Bolt, Semi, or Single?
Also, pics of loads and fired brass help.
 
jrebel said:
Are you jamming the AH hunter in the lands. Make sure you have a big enough jump. I now start my seating depth at 0.05" where as with cut and core bullets I started them at 0.02". These mono's do not like to be close to the lands and will create a huge pressure spike....like dangerous pressure spike!!! Check your seating depth and make sure you are not close to the lands.

I know this because I had the same problem with some HHT's in my 300 wsm.
Click to expand...
Right now I'm 30 thou off the lands. I will try further out, but 30 thou is not causing the pressure I'm seeing
 
riceman said:
Legend,
Can you give us a bit more information on your load. Primers, powder charge, coal, brass, etc.
This will help us with a direction that can possibly lead to figuring out what is going on.
Thanks
Click to expand...
Sure: tried new alpha SRP brass, 44 gr of varget, BR4 primers, seated 30 thou off the lands (coal 2.800), .002 and .003 neck tension, got to 2540 fps and this:

unnamed (1).jpg

Same load, but with 44 gr of 8208 XBR, got to 2665 fps and this:

unnamed (2).jpgunnamed.jpg

Primers looking like this:

unnamed (3).jpg
 
Best I can tell from the pics, and I am by no means and expert, I see swipe but the brass and primer appear to be fine. Again, I might be missing something.

Suggestions that might not be helpful:

I take pictures through a lot magnifying glass that is on my bench. Also helps me to see better. Aging eyes and all…at the ripe old age of 43. Geez.

Have you checked to make sure the chamber/throat and bolt face are clean?

Hope you get it figured out.
 
Can’t explain the swipe. Primers look good. I didn’t try 8208, but here’s my ladder with Varget in a 22.4” Tikka. This same gun got over 3100 fps with TAC. I’d say your velocities aren’t that slow with 16.5” barrel.
 

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aratliff said:
Best I can tell from the pics, and I am by no means and expert, I see swipe but the brass and primer appear to be fine. Again, I might be missing something.

Suggestions that might not be helpful:

I take pictures through a lot magnifying glass that is on my bench. Also helps me to see better. Aging eyes and all…at the ripe old age of 43. Geez.

Have you checked to make sure the chamber/throat and bolt face are clean?

Hope you get it figured out.
Click to expand...
Thanks for the response. For what it's worth, the primers are a little flattened and cratered, but this gun craters pretty much everything, even every factory load I've ever tried in it. Once decapped, I can see the primers are a little mushroomy as well. None of this is captured very well in the pictures, but also none of this is severe. The flattening is not completely flat, the craters are bad but they are always bad, and their isn't any carbon seeping up the side of the primer walls.

I had just done a full cleaning on the gun before this pressure test, so it was probably pretty clean. That said, I don't know much how to clean the chamber throat area. I stick a 410 shotgun cleaning mop in there as far as it will go and rotate it in the chamber, and then just clean the barrel with a guide and dewey rod. Gun only has 150 rounds on it and I've cleaned it every fifty or so rounds.
 
Koda said:
Is Alpha brass typically softer than others?

I sometimes wonder if soft brass leads to false ejector and swipe marks....
Click to expand...
That's a good thought. I'm not sure if alpha is soft. I get pretty early pressure signs on lapua brass as well, and I think they say that is pretty soft
 
LightTheTower said:
Can’t explain the swipe. Primers look good. I didn’t try 8208, but here’s my ladder with Varget in a 22.4” Tikka. This same gun got over 3100 fps with TAC. I’d say your velocities aren’t that slow with 16.5” barrel.
Click to expand...
Good to know and thanks for posting. Only reason I'm confused as to the velocities is that I can get 1950 with the 137gr hammers and AR comp, and 2600 with 165 partitions and varget/AR comp, and the absolutes are supposed to have more velocity than any of them. It's something weird that I can't explain with either that bullet or maybe the alpha brass
 
Legend said:
That said, I don't know much how to clean the chamber throat area. I stick a 410 shotgun cleaning mop in there as far as it will go and rotate it in the chamber,
Click to expand...
Find a brass brush about the diameter of your case, i use a 45acp chamber brush seems to fit... use solvent and twist. I follow up with a chamber mop like you described.
A next caliber brush is good for the throat area to prevent carbon ring buildup...

Edit, speaking of which have you checked for a carbon ring?
 
Last edited:
Legend, a few more questions.
1, Is brass new or previously shot?
2, cases clean? Lube left on new case not previously formed can slip in chamber and "slam" into bolt face giving false swipe(extractor mark) on brass. Clean them with alcohol on a rag. Chamber clean and dry no lube. This grips case before any sliding in chamber. Found this out on a marginally loose chamber.
Just a bit to mull over.
 
To add to riceman, I use alcohol, as a last step after everything, on the chamber to make sure there is no residue of any kind leftover. I use a "sealing" rod guide and still end up with stuff on the chamber walls.
 
Koda said:
Find a brass brush about the diameter of your case, i use a 45acp chamber brush seems to fit... use solvent and twist. I follow up with a chamber mop like you described.
A next caliber brush is good for the throat area to prevent carbon ring buildup...

Edit, speaking of which have you checked for a carbon ring?
Click to expand...
riceman said:
Legend, a few more questions.
1, Is brass new or previously shot?
2, cases clean? Lube left on new case not previously formed can slip in chamber and "slam" into bolt face giving false swipe(extractor mark) on brass. Clean them with alcohol on a rag. Chamber clean and dry no lube. This grips case before any sliding in chamber. Found this out on a marginally loose chamber.
Just a bit to mull over.
Click to expand...
Responses to the above:

Have not checked for carbon ring and don't really know how without a borescope. Gun has only been fired 150ish times and I was hoping not to worry about this in that few shots, but I figured it would come up.

Brass is new, clean.

On number 2, is the point that any residue in the chamber could increase pressure? That makes sense, I'm sure its possible that some oil or borecleaner gets left in my chamber. I can try to knock it out with alcohol

Thanks all
 
Legend said:
Have not checked for carbon ring and don't really know how without a borescope. Gun has only been fired 150ish times and I was hoping not to worry about this in that few shots, but I figured it would come up.
Click to expand...
its not likely then with a newer gun, I just didnt know how new so it was worth asking. If the throat is never cleaned it can build up a carbon ring which raises pressure.... Borescopes are cheap, Id still get one anyways especially for a quality gun or new gun it will really show you how well you clean the bore and chamber condition, Ive heard excessive oil in chamber can cause pressure but I cant imagine whats left over from cleaning to be an issue. A dry chamber test wouldn't hurt here...

Hard to say whats going on. I suspect soft brass /false pressure signs. Ive got a 280ai load thats left an ejector mark now and then otherwise no pressure sign and Im also not getting the velocity I expected with its Absolute bullet. I stopped where its at, whats odd is the ejector mark is on Peterson brass which IMO isnt soft so maybe I (we) have chambers on the smaller end of tolerance and it just is what it is.
 
Yeah, I do think my chamber is tight. My 3x fired brass only neck sized is hardly any different in size from my FL resized and new brass other than it grows a lot. But I would think a tighter pressure would up the velocity with less powder, so even if I hit pressure early in terms of amount of powder in published loads, the velocity would still be there.
 
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