[Scorpio]

I just finished reading an article about some guy who upgraded his RAP. One of the things the writer mentioned is that he put an $800 barrel on it that was headspaced for a specific factory ammo load. He could shoot other ammo in the barrel (not as accurate though) , but with the headspacing set for this specific off the shelf ammo. He must be doing something right because he was repeatedly making one ragged hole with five round groups.

So, I guess my question is this. Is headspacing for factory ammo a common thing? Seems like a way for competitive shooters to avoid getting into reloading. It got me to thinking, would I benefit from having my SPR barrel headspace set for the OTM 75gr 223 I shoot? If I did do it, how would it affect the other loads I shoot like 62gr and 69gr?

 

[stand tall]

Head space is the distance from the back of the case ( case head ) to the datum line on the case shoulder in relation to the bolt face and the chamber datum line. When the case is seated in the chamber and the bolt closed the datum line comes to rest in the chamber, the bolt face is what keeps it from moving back away from the datum line in the chamber and the chamber datum line cut is what keeps it from going forward.


To much space and it's a no go and to little space will not let the bolt close.

More info would be nice, head space is not usually set for a particular load.
But more likely for the proper function of the Datum line to breach face relationship.

If you were shooting 1/2" groups at 100 Yds. I would say that whatever you did might close the group 1/32" each little thing done correctly shaves little bits off the group size when your shooting that good.

Shooting 1 1/2" groups and I doubt you going to notice anything.

Not enough info about you and your shooting or exactly what this guy did.

Head spacing does for factory ammo does not make sense to me, not with the great variances in the ammo, it's made to fit any ones chamber that is book speck and not custom to any one rifle. Perhaps some ammo that is held to extremely tight tolerances.

Then again your info is not complete, makes me want to delete the whole post but you may find something of interest in it.

 

[Varminterror]

Are you certain it was headspaced, or was it throated for the certain round?

It's very common practice to have your chamber cut to fit the chamber dimensions, especially throat leade, to match your desired dimensions and desired bullet.

Target shooters start with the bullet we want to shoot, then design the chamber, barrel twist, and barrel length around that. That's very common.

I'd venture it to be a fool's errand to design a custom rifle around factory ammo. Lots of shooters with a custom rifle can shoot ragged hole groups at 100yrds.

 

[Scorpio]

Are you certain it was headspaced, or was it throated for the certain round?

It's very common practice to have your chamber cut to fit the chamber dimensions, especially throat leade, to match your desired dimensions and desired bullet.

Target shooters start with the bullet we want to shoot, then design the chamber, barrel twist, and barrel length around that. That's very common.

I'd venture it to be a fool's errand to design a custom rifle around factory ammo. Lots of shooters with a custom rifle can shoot ragged hole groups at 100yrds.

The impression I got was that the chamber was milled to fit one specific round like a glove. It was a Hornady 308 load for long distance shooting.

 

[Varminterror]

Since you mention the 308win, did the article reference Palma matches?

I would recommend - having built a lot of rifles and spent a lot of time on a firing line and even more time talking and trying to learn from guys that make a living throwing bullets at targets for a living - that unless you're shooting Palma matches, "custom chambering" to a factory round is a fools folly.

I'm sure it'd be better than using a SAAMI standard chamber if you're using factory ammo, but it's really hard to have a custom barrel in a well built rifle that doesn't shoot bug-hole groups with precision loaded ammo - even if it came in a factory box. Custom rifles shoot well, so why wouldn't a custom rifle shoot well with factory precision ammunition?

But the guys that shoot competitively for a living don't shoot factory rounds (except Palma shooters), it simply costs too much to shoot that volume through factory boxes, and a guy can wring a lot more accuracy out of their brass by reloading.

Take that bughole shooting rifle out to 300yrds and see what it does. Proper competition rifles will shoot bugholes at 200yrds too, some even so at 300yrds. Range records at 1,000yrds are generally under 3" - you're talking about a 0.3" group at 100yrds or less, and under 1" at 300yrds. I have had a half dozen or more rifles - two Savage 12BVSS's in 223rem - that would shoot sub-0.2MOA groups out of the box with factory ammunition. I put together an 18" AR-15 for under $1000 this winter that shoots bugholes at 100yrds with super cheap Rem UMC 50grn JHP's - shooting bugholes isn't that difficult nor uncommon for custom built rifles.

I wouldn't say this guy had any stroke of brilliance. Competition shooters have been matching their chambers to their ammo for decades - and there are plenty of competitions that have rules in which ammunition is provided, or factory ammunition must be used (i.e. all rimfire competitions!!!!), such that custom barrels are specified and chambered to meet the ammunition. Like I said before - we ALL start with the bullet we want to shoot and the velocity we think we can push it with the cartridge we want to carry it...

 

[Scorpio]

I went and re-read the article. This is all it says about the custom barrel mounted on the RPR..

We changed out everything available to us at the time.

Barrel - Custom LongRifles Inc K&P rifle cut barrel chambered for the Hornady Factory 140gr AMAX round

This was the result.

One hole 5 Shot group at 100 yards with Factory Hornady 140gr AMAX bullets. This was the reamer used by LRI, it's why we change barrels out, not only this but the ability to handload and create a variety of good shooting loads.

 

[Varminterror]

I would bet that the "chambered for the Hornady Factory 140 Amax round" is referring to the throat and leade, not specifically the headspace. Hornady's loads are spec'd to SAAMI chambers, such that the headspace will have a 1.630" minimum to 1.640" maximum headspace length with a 0.400" ID.

However, most factory chambers are cut with generous throat diameters to ensure reliable feeding and safe operating pressure, with a generous leade to allow a broad spectrum of bullet weights, which takes away control from the factory ammo shooter over the bullet jump. If a guy knows the throat diameter spread of the factory load and the ogive length on the bullet, they could chamber their barrel to match a factory load.

That's how we build chambers for any custom rifle. You order your reamer to match your desired bullet you'll be shooting, and dies to match it. Why a guy would choose to do so around factory ammo escapes me - why pay two or three times as much for ammo?

 

[BassMan]

Lots of people like me who endlessly play around with rifles have tendencies to fuss around with reamers and resulting chamber dimensions.

The attached is a good read on the subject:

An Introduction to Rifle Chambers

If it is a SAAMI dimension round there should be a SAAMI dimension reamer to closely match the SAAMI dimensioned cartridge.

Additional fussing or playing around with ammo production will usually involve neck turning or inside neck reaming and headspace control by selecting shell holders of certain heights or die adjusting. After that bullet seating depth follows.

If it is not a SAAMI cartridge, a wild-cat, custom reamers and dies are required or in the case of popular wild-cats like the 6.5-06 usually reamers and dies are available off the self. Knowing this the end user is expected to be know about neck sizes and head space.

In the case of loading ammo for any round as soon as it is fired and subjected to pressures of 60 thousand (plus or minus) psi is becomes unique to that chamber and unless full length sized will remain so. At this point should the shooter want to squeeze more accuracy the brass will be neck sized only. Head space will decrease upon only neck sizing, making it necessary to full length size for easy chambering. I full length size each time because the loaded rounds slide into the chamber easily enabling me to shoot successive shots rapidly. I use Forster full length dies and have Forster enlarge or hone out the neck portion to minimize neck work hardening. The Forster dies very closely match SAAMI dimensions of my standard SAAMI reamer.

I imagine the LRI reamers also are a close match for the factory Hornady 6.5 CM ammo.

Shoot the rifle a moderate amount and the throat and leade will be toasted away making efforts to exactly specify these characteristics in a reamer useless after a certain number of rounds fired.

The 6.5 CM is a beautiful cartridge capable of wonderful results in the hands of a talented rifleman and assembled by talented gun smiths and using carefully crafted and assembled ammo.

Look at the attached link to see SAAMI standards for the 6.5 CM - a more perfect 6.5 round for 2.8 inch long magazines.

SAAMI