May 25/04 Test. Using 117gr FB Sierra Pro Hunter bullets Moly coated. CCI Mag primers once fired RWS full sized cases. *
The following modification were made prior to the below test.
1. A rubber washer was fitted in the forearm and the forearm free floated.
2. The fore arm plastic hinge was solid bedded for one inch to the barrel with Brownell Steel Bed.
3. The whole forearm was then bedded with expanding foam. (DOW Great Stuff)
4. The underlug was shimmed on both sides to remove all lateral play.
5. The latch was honed for 100% engagement and solid lock up.
6. Polish the full size die body and shoulder for size of .442" at the shoulder.*
7. Size cases with expander button removed. This will enhance pressure build up in the case*
Hodgdon Manual list's the 120 gr SFT SP 55.5 gr H 1000, Vel. 2902 in a 24" barrel @50.6 kcup.
Estimated vel with the same powder charge and an 117gr bullet is 3042 ft/sec in a 26" barrel.
1. 3- 57.0 gr H1000 av. Vel.2874 ft/sec SD 42 ft
2. 3- 58.0 gr " " " 2932 " " " 29 ft** estimated 48.8kcup. This is a well-balanced load in this rifle.
Alliant Manual lists 52.5 gr Reloder 22 with a 120 gr BT 3080ft/sec at 60.4 kpsi in a 24" barrel a 26" barrel would be about 3160ft/sec.
4. 3- 51.0 gr Reloader av. Vel. 2852 SD 48 ft
5. 3- 52.0 gr " " " 2905 " 125 ft
6. 3- 54.0 gr " " " 3001 " 47 ft
7. 3- 56.0 gr " " " 3160 " 36 ft Most accurate load. Estimated psi 58.2kpsi. ***
***Load #7 all three cases failed to eject and the action opened on all three shots. This load is too hot even though 3160 ft/secit is not a hot load in other 25-06 rifles, which can safely operate at 60 kpsi (SAAMI max).
To get the same velocity 3.5gr of extra powder or 6.2% is needed because of the loose bore.
It seem as though the latch opens when near SAAMI max pressure.
By design-----???
**All loads produced only vertical groups from 2" to 4.5", some you could run a ruler through all three shots. The culprit for the vertical strings is I suspect the barrel latch, which is sliding out with the uplift pressure created by under the barrel hinge pin lock up. Various OAL was used for best results, non was better than the other.
Three things I found are the lube on the latch is a no-no, and the bottom of the latch is radiused and the thumb lever return spring is not stiff enough to keep the latch in place when the rifle is fired.
Under various load conditions the latch moves causing the vertical strings.
I know that various positions of the forarm on the front bench pedestal will cause some vertical groups but not two or three inches with proper bench rest set up.
While I had the action apart I installed a stiffer latch spring, removed a little metal from the front of the thumb lever to make sure the lever will not hold the latch back. The trigger is now a dandy at 25oz. The trigger return spring was reduced to 9oz. The trigger job is very tedious work, and frustrated by the multi times disassembling the action. One better has patiance. Specially when like me you don't know what you are doing.
The hole in a wood block as a guide for the pin punch is not so good because you can't see into the hole. I used a piece of 1/4" plexyglass and drilled 3/16" holes, exact size of the pins, easy to see and center.
One other thing I will do is to place a small dimple of Brownell's Steel bed on the barrel latch recess; this will give the recess some bite for better latch adhesion?
I wonder how that plastic trigger guard will stand up? It looks like pretty tough plastic.
Well I hope now that the rifle will shoot some half-arse groups.
Fred M
