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260 help.... the pressure is on!

I

idaho1

Sergeant
Full Member
Minuteman
Oct 10, 2011
379
3
61
North Idaho
I have been trying to work up an optimal load for my new AIAX 260 24" barrel and am pressuring out at what seem like low level loads compared to other guys on the hide with the same rifle.
At the suggestion of many, I am using H43350, SMk 142's, Lapua brass and federal 210 primers.

The hottest load that worked without any pressure signs (stuck bolt/hard-to-lift bolt) was the following.

41 gr H4350
142 gr SMK
COL 2.80
federal 210

This load only chrony's 2605 fps. I took the load to the range and field tested it out to 850 yards. It took 7.7 mil hold with a 100 yards zero. (3000 foot elevation,30.13 BP, 40 degrees).
The ballistic fte program calculated my true velocity at 2613 based on field data.

Any Idea's for me on why I'm unable to achieve similar velocities as other guys with the same weapon and pressuring out at loads that are slower than factory Cor-bon and factory Black Hills as reported in a review of same? A fellow hider (very experienced) said his go-to load for his AIAW 20 26" was 40.7 H4350, 142SMK and got 2830. I realize he had a 26" barrel and mine is 24" but to lose 225 fps with .3 gr more powders makes me concerned I am doing something wrong.
 
idaho1 said:
H43350
Click to expand...

Well there's your problem! We all use H4350!

Kidding, but yeah you're way low on powder. I run the same load but with Nosler brass at 43.5gr. I'm getting 2812 fps out of a 22" Rock Creek. Are your bullets jammed or jumped? Jamming will cause higher pressure (not as much as you're saying but definitely higher then jumping). Man you got me on this one, that just doesn't make much sense. Gonna have to think about it for a few
 
idaho1 said:
I have been trying to work up an optimal load for my new AIAX 260 24" barrel and am pressuring out at what seem like low level loads compared to other guys on the hide with the same rifle.
At the suggestion of many, I am using H43350, SMk 142's, Lapua brass and federal 210 primers.

The hottest load that worked without any pressure signs (stuck bolt/hard-to-lift bolt) was the following.

41 gr H4350
142 gr SMK
COL 2.80
federal 210

This load only chrony's 2605 fps. I took the load to the range and field tested it out to 850 yards. It took 7.7 mil hold with a 100 yards zero. (3000 foot elevation,30.13 BP, 40 degrees).
The ballistic fte program calculated my true velocity at 2613 based on field data.

Any Idea's for me on why I'm unable to achieve similar velocities as other guys with the same weapon and pressuring out at loads that are slower than factory Cor-bon and factory Black Hills as reported in a review of same? A fellow hider (very experienced) said his go-to load for his AIAW 20 26" was 40.7 H4350, 142SMK and got 2830. I realize he had a 26" barrel and mine is 24" but to lose 225 fps with .3 gr more powders makes me concerned I am doing something wrong.
Click to expand...

First off, all barrels, chambers and bores behave differently.

Maybe you're not bumping your shoulders back enough and you're getting a sticky bolt, not due to inherent pressure, but due more to a headspace issue?

I loaded 260R for a buddy years back and <41.0grs is pretty light, so you might have a different problem, besides thinking that your load is too hot.

What other pressure signs, if any, were you reading?

I neck size my 338LM and shot a box with Norma cases last month, that used my standard pressure load and I had to hammer my bolt open, practically. Another box of the same load, with Lapua brass, which had also been NSed over the last 4-5 cycles, the bolt released more easily.

Moral of the story: it's time to anneal and bump those shoulders back.

Chris
 
All barrels/chambers react differently, but I don't believe for a moment your friend gets 2830fps from a 142smk @ 40.7gr. Nope.

What brass are you using?

Loaded neck diameter?

Fired neck diameter?

Brass length?

Nicely deburred?

Loaded cartridge "headspace" measurement?

Fired cartridge "headspace" measurment?
 
I run 142 SMKs over 42.8 gr of H4350 in R-P brass. That gives me 2760 fps from a 24 inch tube.

One thing that caught my attention was your overall case length. 2.800 is pretty short, which pushes the long bullets down into the case. The end result is less case capacity and a smaller combustion chamber which yields higher pressure.

Without knowing your chamber and throat dimensions I cant safely recommend an OAL to use, but I run an OAL of 2.836 with the SMKs. This keeps me 0.030" from the lands.

The Hornady case gauge/comparator set allows you to measure the OAL to the lands in your rifle with particular bullet. I find it to be very helpful and highly recommend getting one.
 
OP, any idea what barrel is on your AX?
Reason I ask is, over here in the UK, AI use border barrels, and back in December 2011 my mate had the very first .260 AIAX in the country, (had to special order it and wait for a few months because the AX hadnt been up and running very long, and they were busy cranking out military orders)

When he got it, we immediately started development on 140amax/140vld loads, but ran into the same problems as you.
Early pressure, and low velocity.
(All test loads were very accurate, but disappointingly slow)

We managed to get a decent load worked up at 2700fps, about 42.grn of h4350 in the end, (the barrel speeded up after about 100 rounds thru it)
He ran it thru 2012 competition season, and has just swapped it out for a new 20" barrel (border barrel again from AI factory)
And this one is pushing out 140amax about 2760fps with nearly identical charge!

Maybe you have a slow barrel like he did first time around? How many rounds have you put through it so far? You might gain another 50fps as it starts to bed in.
Even though it was slow, it was always super accurate, and he had a very successful comp season with it!
 
I experienced major neck tension issues with virgin Lapua brass causing severe pressure signs.

If you are using brand new brass, try FL sizing then let us know how things go.

That did the trick for me...
 
Thanks guys for the good thoughts/ideas. I will try these out this weekend.

Additional info:
~The barrel is stamped AINA which I believe makes it a Bartlien barrel.

~It holds sub MOA out to 850 yards... the furthest I have shot it to date.

~I now have 200 rounds down the tube and I have to admit it cycles very smoothly now whereas even at 41 gr, during the load work-up phase, even 41 gr seemed sticky 1/5 times.

~the ONLY pressure signs I have noted was sticky, hard to lift bolt. Some cases had extractor gouges visible on the rim of the base of the case.

~I full length re-sized with Forstner dies
~I loaded and shot a hundred rounds with virgin Nosler brass after I worked up the load and had zero issues with sticky lift but I was using the 41 gr load

Thank you guys a lot for the help!!
 
Idaho, have you built a dummy round to find the aol to your lands? With this knowledge you may be able to get some more speed from your loads and retain the accuracy.
 
Rthur said:
Idaho, have you built a dummy round to find the aol to your lands? With this knowledge you may be able to get some more speed from your loads and retain the accuracy.
Click to expand...

No, I have not. I have tried to buy the Hornady version cause I have one of their guages. All my local suppliers are"out". I guess if I knew the thread size of the hornady gauge, I could make one... good idea.
 
Also make sure that your chamber has no residual cleaning byproduct or oil, as that can cause the pressure signs as well. If there is oil on the outside of the bolt, it can get some on the cartridges in the magazine as well.
 
Hmmm, could left over "One shot" case lube residue lead to pressure issues? I usually do not wipe down freshly loaded cartridges.

bricktop said:
Also make sure that your chamber has no residual cleaning byproduct or oil, as that can cause the pressure signs as well. If there is oil on the outside of the bolt, it can get some on the cartridges in the magazine as well.
Click to expand...
 
I'm interested in what you find out, I just shot my first 25 rounds in a ladder test for my new 260 tooley barrel in my ai.
140 amax
42.5gr 4350
Loaded to mag length cci primers and no signs of any pressure at all.

The only thing that jumped out at me was when I switched my barrel my go gauge passed and then failed no-go, added one layer of scotch tape then it passed. Maybe these chambers are a little long? I theoretically have the same barrel but a 26in.
 
I have no explanation but a similar experience with a Lilja barrel in .260. It shot 123g SMK's with H4350 accurately, but slowly. I overcooked a couple of hundred rounds of Lapua brass before backing the charge way off. I never got close to what I thought I should have been seeing.

I recently switched to 142 SMK's and immediately got velocity numbers I liked, even a little faster than expected with H4350. I have no explanation other than "guns are weird".

Best of luck.
 
If "One Shot" is inert it wouldn't lube the sizing die the first time. There will be some residual lube on the case body. Some will transfer to the chamber. It may not build up enough to cause problems...but it can. Clean the cases is my humble opinion.
 
ChrisGarrett said:
One Shot is inert.

So no.

Chris
Click to expand...

Disagree.

Residual lube on cartridges CAN ABSOLUTELY (and often does) create pressure issues.

ETA: A lubricated case doesn't "grab" the chamber, allowing it to shift/flow in ways it doesn't when not lubricated.
 
Idaho, build you a dummy round with your bullet of choice. Make sure you seat the bullet long. Mark this bullet with a sharpie. Continue marking the bullet until you don't see the marks. The lands will leave marks on the bullet until you are seated just short of them. This isn't exact but will give you an idea of your jump to the lands. I have used this technique with good results. Seat the bullet in a few thousandths at a time. This is where a micro seater becomes very handy.

good luck R
 
Rthur said:
Idaho, build you a dummy round with your bullet of choice. Make sure you seat the bullet long. Mark this bullet with a sharpie. Continue marking the bullet until you don't see the marks. The lands will leave marks on the bullet until you are seated just short of them. This isn't exact but will give you an idea of your jump to the lands. I have used this technique with good results. Seat the bullet in a few thousandths at a time. This is where a micro seater becomes very handy.

good luck R
Click to expand...


I've been using this method for quite sometime.... good advice.
 
ChrisGarrett said:
First off, all barrels, chambers and bores behave differently.

Maybe you're not bumping your shoulders back enough and you're getting a sticky bolt, not due to inherent pressure, but due more to a headspace issue?

I loaded 260R for a buddy years back and <41.0grs is pretty light, so you might have a different problem, besides thinking that your load is too hot.

What other pressure signs, if any, were you reading?

I neck size my 338LM and shot a box with Norma cases last month, that used my standard pressure load and I had to hammer my bolt open, practically. Another box of the same load, with Lapua brass, which had also been NSed over the last 4-5 cycles, the bolt released more easily.

Moral of the story: it's time to anneal and bump those shoulders back.

Chris
Click to expand...
Problem solved I think....... It's a brass issue.
First of all I loaded all my "work up" loads in twice fired lapua brass.... Shot in a different 260. These are the ones that I had all the sticky bolt lift issues with.
This afternoon I loaded virgin Nosler brass and shot 43.5 gr with zero bolt lift issues and chronys at 2790!
I don't yet know what is out of whack with the Lapua brass but clearly the rifle can handle 43.5 gr of H4350 without issue.

Thank you all so much! The Hide is a great forum. I was a little bummed before we worked this out to think the rifle I saved for for a long time was going to be a timid slowpoke! Thanks
 
Sounds like you the body of your cases is a shade too big in diameter, and your stiff bolt lift is actually stick icky primary extraction.

To "reclaim" brass fired in a different chamber, I recommend a national match die or small base die.

You should only need to use it prior to the first time its fired in your chamber.
 
former naval person said:
If "One Shot" is inert it wouldn't lube the sizing die the first time. There will be some residual lube on the case body. Some will transfer to the chamber. It may not build up enough to cause problems...but it can. Clean the cases is my humble opinion.
Click to expand...

Inert, meaning it doesn't affect the powder, or primer. He's wondering why he might be getting lower velocities, as if powder contamination was the culprit, or at least that's the angle I was commenting on.

I know One Shot is the Devil, but I've never read of anybody having an issue with exterior build-up on cases, but like you say...anything's possible.

Chris
 
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