AR Barrel Bore Pin Guage

[markm]

Just got a wild hair and gauged both the .223 bolt guns we run, and they BOTH easily pass the pin. The Rem 700 5R has possibly 15-20k rounds through it, and the Tikka has maybe 500 rounds.

Still stumped at why so many of the Chrome lined barrels choke at the first inch of rifling.

[tangolima]

5.56mm (0.219") is the bore or land diameter. 0.223" (5.66mm) is the groove diameter. The latter affects accuracy more than the former.

Groove diameter cannot be measured with pin gauge. One needs to slug the bore for that.

-TL

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[markm]

I love this pin gauge. My problem is I don't know how badly the diameter is. Just that the gauge won't pass through. I can somewhat tell by the velocity spikes which barrels are the worst however.

[Molon]

0.223" (5.66mm) is the groove diameter.

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[tangolima]

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Off by 0.001" (40um). Stand corrected. Not to argue about the tolerance. Thank you for the warm welcome.

Point is measuring bore with a pin gauge serves limited purpose. May get more useful information slugging the bore instead. Cheaper too.

-TL

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[markm]

Point is measuring bore with a pin gauge serves limited purpose.

limited, but massively critical for me. Tight spots are exceedingly problematic.

[tangolima]

limited, but massively critical for me. Tight spots are exceedingly problematic.

Slugging can also identify whether / where there are tight spots, either in the bore or in the grooves. Knowing is perhaps the end of the road. Nothing really you can do about it other than replacing the barrel.

-TL

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[markm]

I've never slugged a barrel so I can't comment on the value of it. But I just need to trouble shoot a few barrels that pop primers on ammo that isn't hot enough to be popping primers.

This $5 gauge gets me some good, basic idea of which barrels that have tight spots and takes 30 seconds to check.

With the pin I don't get the complete story, but I know if I'm barking up the right tree for practically no time or money.

[joedirt199]

I have slugged pellet barrels before and it lets you know if you have a tight spot and also how tight the choke is, if the barrel has one. You can also measure the pellet afterwards and get your diameter since pellets come in several sizes. You would need to find some slugs that would be larger than the barrel. Most .22 slugs are .216-.218. Silicon spray and punch that slug through the barrel.

[lysander]

The tolerance is in the plus dimension. . .