Range Report  DTA HTI .375CT overpressure issues

WaltHer

Sergeant
Full Member
Minuteman
Aug 26, 2009
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601
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hillbilluns, montucky
Hello all,
I am up against a brick wall on this issue and could use some fresh advice. Here goes:
I have a Desert Tech HTI .375 CT rifle with factory barrel and bolt with a custom Elite Iron Windtalker suppressor. I purchased it new in 2014, and had a barrel/bolt failure at 100rounds that was replaced by DT with a new barrel/bolt in late 2014. The current barrel/bolt has 350 rounds through it, and is usually producing groups in the <.75MOA range.

When I purchased the rifle I purchased 200 pieces of new Bertram Brass that I divided into 50 round boxes and have kept together since. I am using the 352 gr CE MTAC solid exclusively. I only use Federal GM215M primers, and have only used one load-as it just worked- 132.5 grains of Retumbo and a COAL of 4.433 COAL. They have all been reloaded using a set of Veirsco full length sizing dies and micrometer seating die. Powder charges are measured with an RCBS Chargemaster, calibrated prior to each reloading session. Brass have been annealed after 2 firings. About 20% of the brass exhibits what I would consider mildly loose primer pockets. No other problems with the brass are observable.

After exhausting one 50 round box ( my box #4/2rd firing) and having excellent results, I switched to another box ( #1/3rd firing, freshly annealed) that I had loaded approximately 1 year ago. (all ammo stored in dry dark place with no humidity). While test firing this box (box #1) and confirming zero the first 3 rounds all felt hot, and bolt lift was heavy. Conditions were about 80 deg F, DA 5700ft. Upon opening the action after each round the primer had been blown out and major scarring of the cartridge base was present. This has never happened before, conditions were normal for me. I discontinued use of that ammo. I then tested 5 rounds from each of the other 3 boxes (2,3,4) and had similar results from 2 of them, and no problems with the 3rd firing of the fourth batch (that I just finished firing when this started and reloading after annealing). I also fired two remaining factory DT rounds with no problem. Lot 4 delivered .75MOA as usual, the two factory rounds were overlapping. The problem lots (1,2,3) were atypical groups >2MOA. Lots 1,2 had velocities of 3175 FPS, whereas my usual MV is 3096FPS. LabRadar problems prevented me from obtaining MV's on lot 3.

Unfortunately, one of the final lot 2 firings was so severe that the bolt's ejector was forced back into the body of the bolt, locking it up. It has now been sent to DT for inspection and repair. I have disassembled rounds from box 2,3,4 and checked their powder charges. They metered exactly at 132.4-132.5 grains. The only unusual thing I noted is that when pulling down the rounds, the powder in boxes 2,3 (loaded in 2016) poured out of the brass unevenly-almost like it was stuck in the bottom of the case- no clumping was obvious once out. The powder in box 4, that I had just reloaded, poured out easily and evenly. As I stated above, to the best of my knowledge no variables in components or conditions should be present. All of the pulled projectiles appeared to have the same dimensions as the newer ones I have yet to reload, and exactly match the one removed from one round of DT factory ammunition.

I don't know where to go with this next. . The only variable that I am completely unsure of is how much-if any- my sizing die is bumping the shoulder of my fired brass. It is still screwed down so that the arm on my press slightly cams over at full extension. I have 200 pieces of new Peterson brass, and another 100 pieces of new Bertram Brass available and 10# of Retumbo from the same lot to experiment with, but am unsure of how to proceed. Any advice would be appreciated. If I left any pertinent details out, please let me know. Thanks in advance.
 
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steve123

Lt. Colonel
Full Member
Minuteman
Mar 16, 2008
9,141
1,631
none of your business
Just curious, how much neck expansion are you getting on the different types of brass? Brass trimmed to proper length?

Did you get any hangfires?

Are you using powder from different lot numbers of Retumbo?

132 grains of Retumbo is what I used to use with 350 Hookers. Reflecting back that load was too hard on the Jamison brass, even the 2star only went 3-4 cycles. if I were to go back in time knowing what I do now I'd do a ladder test at 500Y on a calm day and pick the low node.