Strange pressure

Lawnboi

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Iv got a barrel that’s driving me nuts. Iv now loaded for 5 6.5cm barrels and this one is leaving me scratching my head. This barrel is from hell’s canyon armory, smith work done by him.

Early on I did a ladder with 140 hornady bullets, just to fire form the brass. I saw pressure earlier with this barrel than any other Iv loaded for. Usually around 41 of h4350 is a ways off pressure, in this barrel 40 gave me pressure. Ended up wrecking some brass being it stretched so much. Brass growth for the normal stuff was normal, maybe a bit long around .004” Anyways I loaded down, fire formed the brass then the gun sat. Accuracy with the fire forming loads was acceptable, nothing special. The pressure just left me scratching my head. This is the first creedmoor barrel Iv ever seen make pressure so low in charge. Velocity was right where I expected it, 20”, going around 2600.

Fast forward to today, I load up a ladder with some leftover 140 hybrids. 38.8-41.5 of h4350. Confirmed I wasn’t kissing the lands at Berger factory length of 2.810 and loaded them up. Brass was all bumped back two thou. Note all same lot Lapua brass. Went and shot. Got some odd results. As expected velocity tipped out at 2650.

38.5-39.5 all went normal, very little brass growth. 2500 ish fps
40-40.5 slightly stiff bolt lift, no ejector marks, brass growth +.0025
41-41.5 all normal, smooth bolt lift, no signs of pressure, brass growth back to .0015-.002.

So this leaves me scratching my head, is this something that can happen? Pressure coming and going? This barrel is driving me nuts. Is the headspace messed up? Factory brass was 1.536 to the datum, fired is 1.540 and I’m bumping to 1.538. The pieces that were still were all 1.542ish and were very tight to chamber again. I do note that this chamber allows more brass growth than any other creedmoor Iv loaded for. Most of the time im bumping to 1.536-1.537.
 

Cahunter805

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Oct 8, 2012
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Could be a wide variety of reasons. I would size some brass and retest 40-41.5 and see what happens.
The bore of the HCA barrel could be tighter or the reamer might not be SAAMI also.
 
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Lawnboi

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Could be a wide variety of reasons. I would size some brass and retest 40-41.5 and see what happens.
The bore of the HCA barrel could be tighter or the reamer might not be SAAMI also.
I just measured the throat and loaded a few 140 elite hunters with 41.5 grains. Brass grew .001” and zero signs of pressure. That said the throat on this thing is definetly on the long side. 2.9” and I’m .060 from jam.

So another data point, 2 more shots at 41.5 with no pressure. The 4 other creedmoors Iv loaded for all were over a grain from pressure at 41.5 and 140s. In fact it’s my go to load for my match rifle.

Just strange how 40.5 has consistently, and I’m talking over a couple dozen rounds, shown pressure by only bolt lift and primer pocket stretch, but 41 and 41.5 does not, nor does below that 40 mark.
 
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Lawnboi

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Supposed to be a saami reamer per my receipt

I also wonder if I’d see this with srp brass. The head stamp pressure I’m seeing is only around the primer cup; no ejector marks just a little shiny around the cup.
 
Last edited:

drewturner

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Jun 24, 2021
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You might check the neck diameter of a fired round vs a sized round. I doubt that would be the issue because your pressure comes and goes but I had a creedmoor that had a tight neck chamber and with brass other than Hornady i would get pressure way sooner than it should have. My fired cases and sized cases neck measurements were only .001 diff.
 
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Lawnboi

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You might check the neck diameter of a fired round vs a sized round. I doubt that would be the issue because your pressure comes and goes but I had a creedmoor that had a tight neck chamber and with brass other than Hornady i would get pressure way sooner than it should have. My fired cases and sized cases neck measurements were only .001 diff.
I did check that. A bullet slides in a fired case without difficulty.

I did more digging around and sounds like I may have either a batch of brass that is a little proud in the center, or I have a bolt face that is a hair proud in the center. Being that I am not seeing any other signs of pressure besides a little stiff bolt lift and some shine around the primer pocket I’m guessing this is the case. Im going to keep on firing. Last string of 10 loaded at 41.5 were good, had one that gave me a little shine and the bolt lift stiffness but all other were good.

I also notice that my bolt face had a cerakote on it that has now worn off everywhere but around the primer pocket, next step is to try to polish this off. The cerakote as a whole on this rifle is shit, idk what hells canyon armory did but it’s unlike my other 2 coated tikkas.
 

Wickedpissa

Junior Member
Joined
Apr 17, 2020
Messages
16
Not certain of course but sounds like you have excessive headspace. Get yourself some chamber casting alloy. Doesn’t cost much. Load dummy round in chamber push cleaning rod into muzzle make a mark where it hits. Remove both. Insert rod with tight patch a little farther than mark on rod. Approximately how much bullet shows on the dummy. Heat alloy with torch in reloading pan or something similar. Pour in chamber till full. Sets up almost instantly. Poke out with rod. Measure. Should tell you what you need. Picture is 20 Tactical that was .60 long made this happen
 

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