Contender in 5.7x28

[Ranb]

Since I retired I moved my entire gun collection to MN as my house there is always occupied by my mom or my brother whereas my WA house is only occupied about half the year. I'm already regretting this decision as I have nothing to shooting other than an air rifle and air pistol that are stored at a gun club in Bremerton that I go to occasionally.

My latest project is in pieces in MN. It will be a 14" suppressed Thompson Center G2 SBR chambered in 5.7x28, with a 1-7 twist, for shooting subsonic 70 grain (or similar) bullets. The 5.7x28 is the smallest capacity commercial center fire cartridge that I know of; about 20% less than the 22 Hornet. I have a gallon of the brass I picked up at the range over the last decade. I'm hoping the required powder charge will be between two to three grains of Bullseye. This would allow me to use it with my homemade 22 cal silencer, maybe.


The barrel from Match Grade Machine; $500.


It will look something like my 7mm TCU G2 when finished, but with a scope and a smaller silencer.

It should be significantly more accurate and more powerful than my 22lr rifles at ranges out to 200 yards. I should get about 170 ft-lbs of KE with a 70 grain bullet compared to only 98 ft-lbs with the 22lr. The 70 grain Speer bullet has a BC of .214 whereas the 40 grain bullet in a 22lr is typically about .17, I think.

At subsonic speeds it will not make much of a difference in bullet trajectory out to 200 yards, but the 70 grain bullet will be 20% more powerful at 200 yards than the 40 grain bullet is at the muzzle.

I have a 18" Contender barrel in 22 K-hornet, but it has a 1-12 twist and I normally use 35 grain bullets (300 fps) in it.

[Ranb]

I'm home in MN at last and completed assembly of my G2 SBR. I'll start load development tomorrow when I get the dies. Hoping to stay at 3 grains of powder or below for 55 fmj and 70 semi-spitzer. 3 grains of powder in a 14" barrel should not overwhelm my light weight form 1 silencer.

[Ranb]

I tested two loads today. 55 fmj surplus bullets with Bullseye powder, OAL of 1.65". 2.0 grains of powder gave me 994 fps with a stdev of 13 fps. 2.4 grains got 1150 fps with a stdev of 22 fps. Groups at 50 yards from a slightly shakey rest were about an inch. The standard deviations were disappointing as was the accuracy. But then I've never had good results with fmj bullets made for supersonic cartridges in subsonic loads.

I'm going to try out Speer 70 grain semi-spitzer bullets next. I've had good results with these bullets in subsonic 5.56 in my ar-15. I'll load the 70 grain bullets out to the lands if possible.