Overthinking it? Upper receiver selection choice for accurized SPR build (not a match rifle)
- Thread starter Amatsukaze_DD
- Start date
Here’s my 18” Criterion. ADM upper (required thermal fit), 15 CMT UHPR Mod 1 handguard, Trijicon Credo 2-10x36 with offset holsun 507C x2.
Stripped it’s around 8lbs. With the 10” ARCA and bipod it’s closer to 10lbs.
I’ve used this to hit 2/3 IPSC targets out to 650 off various props.
Stripped it’s around 8lbs. With the 10” ARCA and bipod it’s closer to 10lbs.
I’ve used this to hit 2/3 IPSC targets out to 650 off various props.
TriggerShims makes a lot of different firearm shims, including for ARs. They have bolt catch shims in various thicknesses. I'm not knocking on your shim, just passing along info.Had to shim the Bolt release. Paper hole punch, plastic, drill.
Dremel to the handguard for gas block clearance.
View attachment 8158104
View attachment 8158105
Still well under F-Open weight.
My build (kitchen assembled) doesn't fit the OP's need for a SPR AR.
But, form, fit, function doesn't always follow cost.
Mine is heavy, on purpose. Cheap, on purpose.
This latest one hasn't been shot yet. Hopefully will do OK @ 600.
But, form, fit, function doesn't always follow cost.
Mine is heavy, on purpose. Cheap, on purpose.
This latest one hasn't been shot yet. Hopefully will do OK @ 600.
What bullet you shooting in f open?This will get me called poor
Put together a cheap upper.
$99 BCA side charge (with complete BCG),
$60 Mentium-USA 2 inch diameter handguard 0.936 gas adjustable gas block won't fit under narrow tube.
$350 28" barrel bought as a spare for my 3000 round barrel. View attachment 8158096
So, got the upper together and why not just slap together another lower from spare parts?
Schmid 2 stage, light trigger spring, mil disconnector spring.
80% plastic.
H2 buffer and standard carbine spring.
Clearance TI-7 stock.
Topped with a Buras 8-40X50 from Midway on sale, on a 20 MOA Primary Arms mount.
I see a lot of talk about thermal fit without any real measurements.
How far does the extension slip in before it binds?
Is there a taper to the extension? A real undersize receiver bore will require heating/cooling to put together.
With 7075 having a linear thermal expansion of about 11 micro inches per degree F raising the temperature from 80F to 220F gives about 0.0015" expansion. Cooling 400 series SS with about 6 micro inches per degree F from 80F to 10F gives about 0.0004" shrinkage.
Close to 0.002" if you work fast
When I do mine I go for 240F/4F but the receiver is cooling and the barrel warming.
How hot does that junction get when shooting and is it still thermally joined?
For those that don't like the side charge uppers, there is a rear charge heavy walled upper available (4oz weight penalty) that has more of that 7075 in the body where the extension sits. BUT, it's not thermal fit with most extensions without some compensation.
How far does the extension slip in before it binds?
Is there a taper to the extension? A real undersize receiver bore will require heating/cooling to put together.
With 7075 having a linear thermal expansion of about 11 micro inches per degree F raising the temperature from 80F to 220F gives about 0.0015" expansion. Cooling 400 series SS with about 6 micro inches per degree F from 80F to 10F gives about 0.0004" shrinkage.
Close to 0.002" if you work fast
When I do mine I go for 240F/4F but the receiver is cooling and the barrel warming.
How hot does that junction get when shooting and is it still thermally joined?
For those that don't like the side charge uppers, there is a rear charge heavy walled upper available (4oz weight penalty) that has more of that 7075 in the body where the extension sits. BUT, it's not thermal fit with most extensions without some compensation.
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Will do.
The second one is likely getting a 1-8, so I might not get as good results as its capable. But if my laziness subsides, I may put a large scope on it for some groups.
To be clear, it's small frame rifle, so the comparison to the SLR-equiped 308 may not be helpful. I have a few Mega handguard-receiver uppers, but they are all small frame. Cost notwithstanding, I'd love one for the large frame.
Large frames' have SLR, Wilson Combat mlok, and LMT...
If thermal fit is what you want, any upper can work. If you want a specific configuration in an upper and the extension just slides in sloppy, you can always shim it with some SS stock. I researched it a bit some time back and read some articles by Joe Carlos detailing how he did it. It's rather easy and after buying some SS kits off of a seller on Fleabay, I now do it to every AR I build. I ended up buying .001" and .0015" stock from McMaster-Carr (so I wouldn't run out when I had one being a PITA). Usually after a good heat up of the upper from my heatgun, I still have to give the barrels a tap of two for that last 1/4" or so. I have used the Blue Loctite trick but I much prefer using a SS shim.
The reason I went this way was the particular upper I was using gave a pretty loose fit to the extension. I will not tell you that this effort will make a rifle shoot more accurately but all of mine shoot as well as I hoped for. Of course Proof, Rainier Ultra Match, and Craddock Precision barrels didn't hurt either.
One upper I didn't see mentioned is also a thermal fit (Iron City Hatchet). I prefer a heavy walled upper and I'm no huge fan of a forward assist on a rifle that will be used for targets only.
As I don't mind tinkering, I ended up shimming every complete upper I own
The reason I went this way was the particular upper I was using gave a pretty loose fit to the extension. I will not tell you that this effort will make a rifle shoot more accurately but all of mine shoot as well as I hoped for. Of course Proof, Rainier Ultra Match, and Craddock Precision barrels didn't hurt either.
One upper I didn't see mentioned is also a thermal fit (Iron City Hatchet). I prefer a heavy walled upper and I'm no huge fan of a forward assist on a rifle that will be used for targets only.
As I don't mind tinkering, I ended up shimming every complete upper I own
Well the Craddock barrel is a Bartlein 11" 223 from their Signature Series I believe they call it. It is one sweet shooting barrel. It's still relatively new (less than 300 rounds) but it shoots any of the heavies great, cleans easy, and the chamber looks very nice and smooth.
I have 2 Rainier Ultra Match barrels (1 older Shilen 223 18" and a new Criterion 300BO 10.3"). Unless I read it here wrong, Craddock Precision chambered the 300BO barrel for Rainier and probably fluted it too. As nice as the chamber looks using my Teslong, I'd say it probably was done by them. I have read how much trouble some folks have getting a 300BO to shoot with a 223, but this barrel shined from the beginning. I has never had a factory loaded round through it and I use H110 for subs and supers. This barrel is also less than 300 rounds but cleans as easily as the Bartlein and the inside looks as good as the outside. I use a Dead Air Nomad 30 on both barrels.
I would buy another of each without hesitation and I'm picky and won't hesitate to spend money on my toys....
I should have added both uppers/barrels were thermal fits with the Rainier Ultra barrel using shim stock and the Craddock Bartlein in an undersized upper (Iron City Hatchet), both use a JP bolt/carrier, and share a Aero M4E1 SBR lower.
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Somewhat belatedly... here are a few pics of the Mega receiver and the SLR ZRO hand guard. Note that with the narrow (normal-sized) first 1913 lug, the pin hole is exposed. I a) actually kinda like it, b) don't think it will matter and c) Todd at SLR offered a short pin had I wanted it. The drill jig was easy to use, and the interface seems strong. The pin is larger than the V Seven pins and the Wedgelock pins, but I don't know if thats because its a large frame item.
The MEGA is one heavy walled upper. Thicker than the BCA.
The Old Style MEGA is shown. The new ones aren't quite as thick.
The Old Style MEGA is shown above. The new ones aren't quite as thick.
The Old Style MEGA is shown. The new ones aren't quite as thick.
The Old Style MEGA is shown above. The new ones aren't quite as thick.
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And who among us doesn't want to own something thats "Mega" or "thicker," or...
Im sure I have said too much.
More relevant, I went to the range yesterday and set up the 308. I did a bit of break-in with the Wilson Combat barrel: shoot some/ clean some and used a spare Athlon 5-25 and Labradar just to see before setting up the 1-6 and offset.
For general posterity, For MV's I got:
American Eagle 150 gr: 2695 fps
Gorilla 175gr match: 2473
Hornady 168 gr match: 2552
10 shots each and I didn't keep any data other than average MV.
And while my precision shooting skills are consistently beyond my reach (or consistent precision shooting is beyond...), the first 5 shot group with the 175--and this was with about 25 rounds through the barrel-- was about an Moa group. 2 other groups both had 3 shots touching and then close by 2 shots touching. Had my form been better...
Not scientific, but my guess is that in better hands, and when not brand new, the WC barrel seems quite capable.
Im sure I have said too much.
More relevant, I went to the range yesterday and set up the 308. I did a bit of break-in with the Wilson Combat barrel: shoot some/ clean some and used a spare Athlon 5-25 and Labradar just to see before setting up the 1-6 and offset.
For general posterity, For MV's I got:
American Eagle 150 gr: 2695 fps
Gorilla 175gr match: 2473
Hornady 168 gr match: 2552
10 shots each and I didn't keep any data other than average MV.
And while my precision shooting skills are consistently beyond my reach (or consistent precision shooting is beyond...), the first 5 shot group with the 175--and this was with about 25 rounds through the barrel-- was about an Moa group. 2 other groups both had 3 shots touching and then close by 2 shots touching. Had my form been better...
Not scientific, but my guess is that in better hands, and when not brand new, the WC barrel seems quite capable.
I'm building for a similar application as OP (super amateur-level PRS gas gun in 6 ARC) and I already bought my receiver prior to reading this thread. 6 ARC will likely burn up barrels fairly quickly, so I don't want to bed for ease of swapping in new barrels.
With all of that in mind, does anyone know where Geissele Super Duty upper receivers fall on the receiver/barrel fit spectrum? Do I need to bail on the Geissele and find a different upper receiver for this build? If it's not "thermal fit," how much accuracy am I giving up?
With all of that in mind, does anyone know where Geissele Super Duty upper receivers fall on the receiver/barrel fit spectrum? Do I need to bail on the Geissele and find a different upper receiver for this build? If it's not "thermal fit," how much accuracy am I giving up?
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Everything I can find says to expect <6.5 Creedmoor round counts. I'm taking that to mean <3k-ish round barrel life for precision work. Do I have that wrong?
Also, what's the best way to removed bedded AR barrels? You're basically gluing the barrel into the receiver, right?
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Update : went with a san-tan upper and a CMT UPHR mod4. It's a snug fit barrel to receiver, but definitely not a full thermal fit like san-tan advertises. I will be bedding the barrel with loctite, and hopefully the uphr hg is stiff enough to hold up to bracing and bipod work. Will report back here when I get it fully assembled and a 77gr load developed for this barrel.
It's 2/3rds the powder of 6.5CM and lower velocities. 6 Grendel (the OG 6ARC) has been around a long time and is proven to go 5-6k +.
A vice, wooden dowel and small mallet will get a bedded barrel out easily. "Gluing" is an overly strong way to describe bedding.
Thanks! This is my first time doing this, so that's super-valuable insight. What bedding compound/substance do you use that lets you use the mallet/dowel removal method?
In the past I've used regular old blue and red Loctite. These days I use Loctite 609 as its a sleeve retaining compound, specifically designed to augment press fits. Is it better than blue/red? Not that I can tell, but since the description on the bottle is an exact match to my use it can't be a bad way to go. All of them have disassembled for me easily enough with the mallet method, I once used a little heat on the red and it seemed to loosen it up just a bit.
