Getting Low Velocities........Help me Diagnose....

[wareagle700]

Rifle:
The rifle is a Remington 700 action with a 26" Douglas Premium Air Gaged barrel. The barrel was chambered by Douglas in .260 Remingoton and has a 1 in 8 twist. It sits in an aluminum/glass bedded McMillan A4 with CDI bottom metal.

Load:
140 AMAX
Remington Brass
CCI 200 Primer
41.6gr H-4350
COAL - 2.855 (mag length)
<span style="color: #CC0000">MV - 2675</span>

With this load I can put 10 shots under a half inch consitently at 100 yards. It also remains very accurate at longer ranges.

Problem:
I am getting lower velocities than normal. I am having to dial in 32.5 MOA to get to 1000 yards. Its close to the same dope as my .308. When I see other peoples loads, they are about 200fps faster than me with similar setups. What are some things that could cause these lower velocities? What can I do to speed it up without running high pressure loads?

 

[Hateca]

Re: Getting Low Velocities........Help me Diagnose....

Loose bore diameter, loose chamber dimensions, long throat, environmental conditions, broken chrono to name a few.

Did you actually shoot this to 1000 or are you taking the info out of a ballistic program based off 100 yard data and chrono numbers?

 

[Red_SC]

Re: Getting Low Velocities........Help me Diagnose....

I don't remember my powder charge offhand, but it seems like I'm running several grains more H4350 with 130's. I'm running hBn, though.

 

[FequalsMA]

Re: Getting Low Velocities........Help me Diagnose....

Are you running the moly A-max? Moly will decrease bore pressure a bit. Also some barrels are just slower. The number of grooves, finish, specs, all has a part to play.

Do you jam or jump. A jam will also give more velocity.

Is your powder new?

 

[BobinNC]

Re: Getting Low Velocities........Help me Diagnose....

Well depending on who's data your using, max load is more like 44.5 grains. That could well be the reason your running a bit slow.

As to what you can do to speed things up without running high pressure loads? Well you can change powders, and try RL-17 or RL-19 or even RL-22. H4831 might also be viable. You might try a bullet like the 139 Lapua or even a 130 gr Berger .

You do need pressure to get velocity, try working up in .2 grain increments with your H4350 load.

In the end you may just have a slow barrel. They exist, just like some barrels are fast.

Bob

 

[wareagle700]

Re: Getting Low Velocities........Help me Diagnose....

I have shot it at 1K multiple times. The bullet is not moly coated. I have chrono'd the load 5 times all with the same average (2675). The bullet is jumping .02". The loads I am comparing it to are with the same powder and bullet. I have worked up in .3 increments to 43.3 grains. At 43.0 grains im still only getting 2770fps. I have some loaded up and will try some more tomorrow.
I should add that the barrel is relatively new. (approx. 200 rounds)
Thanks guys. Any more info is appreciated.

 

[bohem]

Re: Getting Low Velocities........Help me Diagnose....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wareagle700</div><div class="ubbcode-body">I have shot it at 1K multiple times. The bullet is not moly coated. I have chrono'd the load 5 times all with the same average (2675). The bullet is jumping .02". The loads I am comparing it to are with the same powder and bullet. I have worked up in .3 increments to 43.3 grains. At 43.0 grains im still only getting 2770fps. I have some loaded up and will try some more tomorrow.
I should add that the barrel is relatively new. (approx. 200 rounds)
Thanks guys. Any more info is appreciated.
</div></div>

1) Don't jam those Amax's. I shoot them in a 260 and a 6.5-06 and they like a small jump (like you've found). I shoot them at 0.010" off the lands in both chamberings.

2) H4350 should be more like 44gr max, keep working up until you get extractor groove growth. IE, load a ladder test and take a set of calipers with you to the range. Measure the extractor groove diameter before firing, record the value, fire, measure again, record the value. When you get 0.001" or more of growth you're over pressure and the case is now junk. This is you max point.

I get about 6-8 loads from my 30-06 brass when I shoot the 208 Amax's from it.

3) With 49.5gr of H4831sc in my 6.5-06 I get 2875 fps avg with the 140 Berger. The same charge, primer, powder, etc. gets me only 2800 with the 140 Amax. The bearing surface on the Amax is longer and creates more frictional drag along the barrel. This is my fire forming load, it shoots bugholes and I've hit steel at 1k+ with it.

4) The Douglass barrels are not lapped after they're rifled. I shoot Shilen's mostly because I get the best price vs. accuracy return on them. They're not lapped either. I hand lapped 1 of my Shilens after I shot 25 rounds through it, when I put it back on the rifle and shot it again the same load was 75 fps faster.

I have an identically barreled rifle on another action that actually got faster between round 25ish and round 200 by almost 100 fps. (Both were shilen CM barrels in 7mm).

So, 75fps from the Amax to the Berger and 75 fps or a lapped barrel gets you much closer to the expected velocities you are looking for. Put some more powder in there and you will probably come up to the 200-250fps you really seek.