Home Forums Hunting & Shooting Ask The Gunwriters What a bore scope can show you

Rather than have this get lost in the two other bore scope threads, I'll post this here.

This is a project gun I'm rehabbing....an Interarms Mark X in 30-06. I'm a sucker for an orphan gun and bought it off the used rack at a local shop.The barrel was full of goo and obviously hadn't been shot much and cleaned less, if at all. Here's what the borescope shows. Borescope used here is a 26" rigid Teslong with the red angled mirror.

#1: Chamber is to your left...you can still see the bluing in the chamber. And then there's this shiny area on the right.


#2: Going further upstream, here we are dead in the middle of the shiny band. Again, the chamber is to your left.


#3: Wading upstream a bit more, the shiny band is on your left and a nice appearing section appears ahead of it to the right...bluing reappears. Note no rifling.

Somebody ream some freebore so they could seat longer bullets out of the powder space?

If they did that it would also push the leade deeper and you'd see the blueing on the rifling would also have been removed.

Al, somebody reaming the neck area to a bigger diameter?

The shiny band is the shoulder area of the chamber. I'm going to test fire a few tomorrow and see what the case shoulder looks like.

Good shootin' -Al

Al, is this a test? Knowing your talent this one is a ground ball for you. Guessing you will set the barrel back and recut the chamber.

While you are at it you will probably blueprint the action, bush the firing pin hole, and install a Timney trigger - just because you can’t help yourself…

No...not a test. Just thought it might spark more people to think about why the shoulder area has a machined finish when the chamber and neck still shows intact bluing.

The ground ball ended up a swing and a miss.

Good shootin' -Al

Well maybe that one had a bit of a tight headspace issue and had to be polished a bit. ?
Always interested in your work sir.
F01

These barrels are hammer forged. That process forms the chamber along with the barrel internals as the barrel material is literally hammered into shape over a carbide mandrel. The barrels are then blued and fitted to the action. Then a pull style reamer that contacts the shoulder area of the chamber is used to set the final headspace. That's why only the shoulder area of this chamber appears as a machined finish.

Many other mfgs use the same process of course but blue the barreld actions together after headspace is set...which is why you don't see the shoulder area of the chamber in the 'as machined' finish.

As always, understanding a process can help us make sense of what we see. This one made me go back to basics when I first saw it.

Good shootin' -Al

Pretty good deduction skills! -Al

🤣🤣🤣
Granddaughter has a bad habit of swinging at really low pitches. She got suckered in to swinging and missed, her coach said to her "okay Tiger, now that you got that one out of your system". I almost fell out of my chair laughing. I returned the favor by yelling at the coach "Ya. even Helen Keller wouldn't have swung at that pitch". 😛

The surface in that image looked flat to me, not angled. I thought maybe someone ran a neck reamer in the chamber but the neck/throat junction didn't look right.

The stripped bolt closed nicely on the 'Go' gauge so off to the range I went. With a max. load of IMR4064 (ok...a bit more than max ), my 150 flat based bullets jammed hard into the lands and a bit of light lube on the cases, it whapped the cases out nicely. Extraction was effortless and the pin strike was well centered on the primers. Chamber neck diameter checks at .343 and the back end of the chamber is nice and snug. Neck runout on the fired cases is right at .001. I had also shortened the barrel 2" and recrowned it and the powder pattern on the muzzle is nice and symetrical.

Good shootin' -Al

Thanks Al. I find your post educational and insightful - keep 'em coming!

Thank you sir. Shortening the barrel on the Mark X pains me a little as they are one of the few who offered a full 24” home for the old ‘06. I’m an unabashed fan of longer barrels and shorter barrels. I guess I’m biased against the 22” length. No real good reasons just my own likes. I really have enjoyed the bore scope threads.
Best regards,
F01

Yes...I would have rather left it at 24" and just touched up the factory crown. Borescopeing showed some issues that made pulling it back 2" a better approach.

Good shootin' -Al

Thanks...appreciate it. -Al

Had no idea the chamber was also hammer forged! Thanks for that information Al.

Not all mfgs. include the partial chamber in the process. Some pull or push the carbide mandrel (that has a short section of rifling on it) along the length of the barrel as it's hammered. Then the chamber is done. Lots of ways for mfgs to accomplish this. If you ever get the chance to see...and hear...the hammer forging process, it's pretty amazing.

Yep!

When Bill Ruger finally decided that the company needed to start making their own barrels around 1990, he did a lot of research and decided on hammer-forging, buying machinery from a company in Germany. The consistency of Ruger barrels immediately improved considerably, but continued to improve: One of Ruger's production honchos told me this was because even though hammer-forging sounds like an "automatic" process, it still requires some experience from the operator(s) for the best results.

All of which is partly why Ruger American Rifles immediately acquired a reputation for grouping very well: RARs appeared in 2012....

Wow, what a safe queen you found there, still blued inside? Not the prettiest final ream, but the bullets won't know that. Good luck, Al, and thanks for the lesson.

The remaining question this inspires to me wonder is: "does that finish affect anything (to practical effect")? I would presume "yes" if one were chasing the finest causes of variation, otherwise it's a "no" to most users. Thanks for posting.