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Posted: 1/1/2007 3:11:06 PM EST
Let me describe my barrel:

The first 0.625" are threaded 1/2"x28 tpi.
The next 0.653" are 0.695" diameter.
The following length is 2.057" long and 0.730" in diameter.
We then step up to a section 1.916" long and 0.750" in diameter.
The next 0.765" are 0.850" in diameter.
From there we have an obvious 45 degree shoulder and the diameter steps up to 0.981" for the remainder of the barrel length. Save the last 2.500" which are a full 1.000" in diameter.

The reason I am asking is because I am considering purchasing the Ops Inc. flash suppressor and associated shoulder. If the numbers above are correct and the Ops gear fits, next Christmas Santa may bring me an Ops model twelve sound suppressor.

I just want to make sure the barrel dimensions are SPR profile for future use.

PS - Please don't gig my measurements - they were performed with a 35 year old Starrett slide calipers. I am not a machinist or an engineer but I did stay at a Holiday Inn Express last night.

SPR or not?
Link Posted: 1/1/2007 3:20:25 PM EST
Courtesy of Randall at AR15barrels.com

Link Posted: 1/1/2007 3:38:02 PM EST

Originally Posted By glock24:
Courtesy of Randall at AR15barrels.com

Randall is no fool...he gives three diameters and one length...that is useful for???

What I need to know is if all my lengths and diameters are SPR profile or not. Thanks for trying to help though. Anyone else?
Link Posted: 1/1/2007 6:15:35 PM EST
Link Posted: 1/1/2007 6:15:42 PM EST

Originally Posted By cszy67:
Let me describe my barrel:

The first 0.625" are threaded 1/2"x28 tpi.
The next 0.653" are 0.695" diameter.
The following length is 2.057" long and 0.730" in diameter.
We then step up to a section 1.916" long and 0.750" in diameter.
The next 0.765" are 0.850" in diameter.
From there we have an obvious 45 degree shoulder and the diameter steps up to 0.981" for the remainder of the barrel length. Save the last 2.500" which are a full 1.000" in diameter.

The reason I am asking is because I am considering purchasing the Ops Inc. flash suppressor and associated shoulder. If the numbers above are correct and the Ops gear fits, next Christmas Santa may bring me an Ops model twelve sound suppressor.

I just want to make sure the barrel dimensions are SPR profile for future use.

PS - Please don't gig my measurements - they were performed with a 35 year old Starrett slide calipers. I am not a machinist or an engineer but I did stay at a Holiday Inn Express last night.

SPR or not?


First of all, most of the barrels out there for sale called "SPR contour" are simply 18" medium contour barrels and are NOT cut for the OPS inc collar. The only production barrel out there that has this feature is the White Oak SPR contour. Compass Lake will make you one that is true SPR contour. But CMMG, Noveske, none of the other "SPR" barrels out there have this feature. What brand to you have? If it's not a White Oak, 99% likelihood that you do not have a compatible barrel.

Many people confuse the simple transition that is cut into most 18" barrels right around the expected location of the collar shelf as being the collar shelf itself, which it is not. The collar shelf is of .010" radius, larger than these transitions which is needed to properly seat the collar and suppressor.

Thirdly, because you plan to use a 12th model suppressor, the correct location of the shelf is critical. To have it too far forward will mean the supressor is not fully seated. Too far back and the brake's mounting threads will be exposed to the blast, which will cause carbon build-up and can lock the suppresssor on to the gun.

If you plan to get the suppressor, I'd buy at least a WOA barrel if not a Douglas from Compass Lake.
Link Posted: 1/1/2007 7:26:01 PM EST
Well, I am confused...first, why would the manufacturer cut these additional profiles into the barrel if they were of no value? This is a $450 barrel from one of the top manufactures...I can't imagine he would waste the extra time cutting this profile just for the heck of it. Why are these cuts on my barrel?

This is not a production barrel but a custom one. I am no expert on AR barrels but it seems to be more of a heavy profile versus a medium one. Would you agree?

Your details regarding the ops collar confuse me...my barrel does step up from 0.730" to 0.750" as you suggest. Randall's barrel profile shows the forward part at 0.730" and we all agree that the gas block sits on a 0.750" area. Mine seems to meet the criteria.

I understand your specifications regarding the position of the collar being too far forward or too far back. But once again...why would my manufacturer cut this step in there if it was of no use?

What are the proper dimensions for an SPR barrel profile?
Link Posted: 1/1/2007 8:01:46 PM EST
[Last Edit: 1/1/2007 8:09:04 PM EST by Onslaught]

Originally Posted By cszy67:
Well, I am confused...first, why would the manufacturer cut these additional profiles into the barrel if they were of no value? This is a $450 barrel from one of the top manufactures...I can't imagine he would waste the extra time cutting this profile just for the heck of it. Why are these cuts on my barrel?

This is not a production barrel but a custom one. I am no expert on AR barrels but it seems to be more of a heavy profile versus a medium one. Would you agree?

Your details regarding the ops collar confuse me...my barrel does step up from 0.730" to 0.750" as you suggest. Randall's barrel profile shows the forward part at 0.730" and we all agree that the gas block sits on a 0.750" area. Mine seems to meet the criteria.

I understand your specifications regarding the position of the collar being too far forward or too far back. But once again...why would my manufacturer cut this step in there if it was of no use?

What are the proper dimensions for an SPR barrel profile?


Just because your barrel is not "SPR" profile, this does NOT mean that your barrel is not set up to accept the Ops Inc. collar.

Now I have NO idea what that dimension is for the collar, but as already mentioned, the "SPR profile" typically just means .840 under the HG to most. You could certainly have a barrel with the Ops Inc. step and be over 1" under the HG.

Actually, the profile of your barrel under the handguards sounds like a typical Bushmaster HBAR to me.

After reading over your numbers again, which "cut" is it you're questioning? All I read is the threaded section, the "grenade launcher" step, the typical barrel in front of the gas block, the gas block, the gas block shoulder, and then the HBAR to the back. Nothing in there seems "extra" our out of the ordinary. Maybe a picture would help?
Link Posted: 1/1/2007 8:26:58 PM EST
[Last Edit: 1/1/2007 9:02:58 PM EST by Homeinvader]

Originally Posted By cszy67:
Well, I am confused...first, why would the manufacturer cut these additional profiles into the barrel if they were of no value? This is a $450 barrel from one of the top manufactures...I can't imagine he would waste the extra time cutting this profile just for the heck of it. Why are these cuts on my barrel?

This is not a production barrel but a custom one. I am no expert on AR barrels but it seems to be more of a heavy profile versus a medium one. Would you agree?

Your details regarding the ops collar confuse me...my barrel does step up from 0.730" to 0.750" as you suggest. Randall's barrel profile shows the forward part at 0.730" and we all agree that the gas block sits on a 0.750" area. Mine seems to meet the criteria.

I understand your specifications regarding the position of the collar being too far forward or too far back. But once again...why would my manufacturer cut this step in there if it was of no use?

What are the proper dimensions for an SPR barrel profile?


You're sort of asking the unanswerable question. The SPR spec has never been published. Those that know the true spec know because they reverse engineered a real SPR barrel right from the source and they want to protect those specs so they can be the go-to guys for SPR barrels. I'm sure your barrel is a good one, but unless OPS inc specifically entered the conversation when you ordered it, I doubt its cut for it.

There is an SPR drawing that gets posted to threads like this and will likely show up here soon, but it is not correct in the collar location or diameter and should not be used if a suppressor is planned. It works fine for most aesthetic purposes, but not for real use.

Do not confuse a transitional step with a load bearing shelf. You'll see these steps in all sorts of contours and they are merely transitions from one diameter to another. It's very difficult and unnecessary to create a smooth taper in a barrel, so when a barrel needs to reduce in diameter a 90 degree step is far more expedient. Buy the OPS brake and collar set and look inside the collar, you'll see the reverse image of the barrel's shelf and this will all be immediately clear to you. Also pay particular attention to the actual change of the inner diameter of the OPS inc collar, there's a slight taper in there which should correspond to a slight taper on the SPR barrel. If your barrel has a straight diameter from your suspected collar shelf to the gas block seat, then there's another indicator.

Link Posted: 1/1/2007 8:52:26 PM EST

Originally Posted By MSTN:
NO - IT'S NOT.


This is one of the few out there with the true SPR specs in hand. A short, but sweet answer to your question.
Link Posted: 1/2/2007 1:54:13 PM EST
PM me your E-mail and I'll send you the drawing. Or you can ask the vendor and see what profile is your barrel and what purpose? LMK.
Link Posted: 1/2/2007 4:04:19 PM EST
[Last Edit: 1/2/2007 4:10:13 PM EST by AR15barrels]
Link Posted: 1/2/2007 4:23:46 PM EST
To everyone - thanks for all the useful information.

When I placed my originial order for this custom barrel I did not specify any type of SPR profile. When the barrel arrived it "appeared" to have an SPRish style profile - thus my questions.

If my barrel had an accurate SPR profile I would have semi-considered an Ops system complete with collar, brake, and sound suppressor. Since my barrel is NOT an SPR profile I can save my money and just install me $25 phantom.

My wife is quite happy now and would like to thank the members that indirectly saved her over $1000.

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