First Group on custom SPR build

[Chorizo]

Below is the first group shot from an adequate rest at 100 yards using factory ammo - HSM 55gr V-max. (40 rounds then thorough cleaning, 15 rounds then group)

Using a Mk12 SPR concept, I built it myself:

Aero Precision upper and lower (I trued the upper receiver face with Brownells receiver lapping tool)
Geissele Hi-Speed Match DMR trigger group
BCM 18" SPR rifle gas 1/8" twist
BCM Lo-profile gas block
Boise Tactical M-16 phosphate BCG
Gunfighter mod 4 charging handle
Kaw Valley Precision Linear Comp
DPMS 12" free float handguard
A2 stock/buffer
JP Enterprises scope mounts
Leupold VX-III 4.5x14x40 SF CDS 30mm tube

.438" (7/16")

http://i158.photobucket.com/albums/t106/chorizo_2007/chorizo/group.jpg (http://s158.photobucket.com/user/chorizo_2007/media/chorizo/group.jpg.html)

http://i158.photobucket.com/albums/t106/chorizo_2007/chorizo/rifle.jpg (http://s158.photobucket.com/user/chorizo_2007/media/chorizo/rifle.jpg.html)

[jmk]

nice rifle. very nice shooting.

what's your impression of the linear comp?

how much work did you have to put into the AP upper to square it?

how's the fit of the upper to lower?

my varmint rig has a solid tube forearm, too. gets really hot after a bit...

thanks for sharing - looks like you know what you're doing.

[markm]

Nice! Those Vmax bullets are lasers.

[Chorizo]

Thank you for the kind words....I learned much of the details from extensive reading here and it helped come precision build time. That was my 5th build.

The linear comp does indeed lower the muzzle blast to the side and rear. I was worried that it may contribute to over-gassing. But my brass landed in a nice neat pile at the 4 o'clock position. As this rifle's "special purpose" will be hunting 4 leg critters, I wanted lower the blast to my partners and me in the field. I like the looks of the Kay Valley comp. I feel it is a keeper.

The fit to the lower and upper is typical AR-rattle. No worse and no better than the average set-up. My readings here lead me to believe that that fit really doesn't matter and the target validates that observation.

The truing of the face of the upper was interesting. It only took very little work and about three 20 second spins with the fine valve polishing compound leaving about 1/3 bare metal and the remainder just starting to lose color, but what is interesting is the following:

I built, just prior to this one a Recce version for a truck gun. I used an Aero Precision blem lower and a regular upper. I taped the threads and duro-coat (bake) the assemblies (upper parts less barrel and lower assembly) in desert brown. I did NOT true the face on that upper. I also used a DPMS 12" handguard on this build. When torquing the barrel nut, I torqued to 35 foot-pounds X3 using choke anti-seize grease and the gas tube hole lined up perfectly at 35lbs on the third run. The SPR build, using the same technique and equipment, on the third run, it stopped at 35lbs past a line-up and to get to the next hole took just at 55 lbs of torque. Significant????? I don't know, just an observation. I backed off and did X3 at 55lbs and all seated and lined up fine.

DPMS makes a ventilated tube, I may buy it and screw it on (without taking the nut off) down the road if it starts to get hot to hold, but with the pace of shooting critters, even on whistle pigs, I doubt I will get it too hot. I wanted to keep crap out of there more than I wanted cooling properties. I walk through lots of tall sagebrush and don't want sticks poking in there.

I am happy with it. I will take a real sandbag setup out next time and see what I get.

[polymorpheous]

3 round group?
Really?

Shoot 10's or at least some 5's.

[Iraqgunz]

A few critiques here. That tube is going to get very hot in any situation where you start to fire multiple rounds.

I would also echo what Poly said. You need to shoot a few 5 or 10 round groups in order to get any type of true accuracy potential. When markm and the AZ crew goes out, we almost always shoot a minimum of 5 rounds and we usually do a few different strings.

[Chorizo]

3 round group?
Really?

Shoot 10's or at least some 5's.

I guess I am not as manly as you are. I alway heard that if you do the first one right, you won't need to shoot a bunch more :D

Great suggestions, I will do that next time out. A few 5 shot groups and multiple strings are in order. When shooting the 40 round to break in the barrel it did not get as hot as the Recce. I hunt mostly cool weather for multiple rounds (sage rats in the spring) so I will wait until I observe an issue before changing out. The Recce handguard will be swapped out for a Rock River TRO free float and I will likely get the vented tube for swap out if I am going out for a big shoot day.

My first shot is what I am normally concerned about.

http://i158.photobucket.com/albums/t106/chorizo_2007/chorizo/dot.jpg (http://s158.photobucket.com/user/chorizo_2007/media/chorizo/dot.jpg.html)

[Chorizo]

IG, as an aside, at what point does the heating of the gas tube become an issue? I can see my recce having problems in a defensive use situation, but in a hunting, slow fire situation, will the SPR reach the critical point?

Now you got me handwringing.

[polymorpheous]

I am in no way, shape, or form... manly.
:lol:

[jaxman7]

I am in no way, shape, or form... manly.
:lol:

There is a remedy for that poly. Just start chewing tobacco. ;) Ya know.... cures slack jaw and makes you a Tyrannosaurus.

-Jax

[Iraqgunz]

When I say tube, I am referring to the rail. Those things heat up rather quick.


IG, as an aside, at what point does the heating of the gas tube become an issue? I can see my recce having problems in a defensive use situation, but in a hunting, slow fire situation, will the SPR reach the critical point?

Now you got me handwringing.

[Chorizo]

Thanks, IG. I will keep an eye on it. Likely will order a vented tube from DPMS. It is shooting so well, I don't want to touch the barrel nut.

[DiabhailGadhar]

First off Semper Fi and welcome...secondly, rock river arms, DPMS?!?!?? There are far better options out there. But a nice looking rifle for sure.

[themissinglink]

Nice setup, just some fine tuning and it should be a fun shooter.

Seems to be fairly accurate.

[Chorizo]

First off Semper Fi and welcome...secondly, rock river arms, DPMS?!?!?? There are far better options out there. But a nice looking rifle for sure.

S/F...thanks for the welcome and the comments on the rifle.

The SPR doesn't have any Rock River on it, just a DPMS free float.

I liked the DPMS tube feel......This is a hunting gun, I didn't need any tacticool on it.

I looked at the other options and they didn't fit my "mission" needs. I am not hanging crap off of it other than a bipod occasionally for bench shooting.

As for tuning it, I am quite happy with that group for factory ammo. I have 2000 rounds of it and I got out of the reloading business as it is too time consuming for me. As MarkM said, V-Max are like lasers. I think I can get a better group with a real sandbag setup after it has had a little more break-in.

But just for the hell of it, tell me what is wrong with the DPMS free float tube that would make me want to replace it.