Best material to machine pin gauge set from?

[Markit]

I need to measure my receiver raceways prior to ordering an oversize bolt from PTG for a used savage rifle I purchased sight unseen that has a bolt with excessive play (I am an idiot for breaking my rule of never buying firearms sight unseen and will not do so again - 2nd time I have been burned).

I plan on machining my own pin gauges after measuring the raceways with calibers to get a rough idea of sizes to machine. I just can’t stand the thought of paying over a hundred dollars for something that takes 10 minutes to turn on the lathe.

Is there any preferred material to use for pin gauges?

I have scraps of rod in the following: 6061 Ali, mild steel, brass, and bronze.

I also have a swack load of scraps of engineered plastics like Delrin and acetal.

Does it make a difference what material I use?

Will likely only need to measure one rifle for raceway ID so would prefer not to waste bronze or brass given the cost.

Lastly, do you use lube on the pin gauges prior to measuring raceways or do you insert them dry to get a more accurate measurement.

Any input from a gunsmith or someone who has measured raceways or machined pin gauges for a similar application before would be appreciated.

Many thanks in advance.

Markit

 

[Potashminer]

I can't help but will be following this thread - I was under the impression that pin gauges were ground to diameter. If they can be turned on a lathe, I have a lot of practicing to do!! I suppose it is all in the required tolerance? +/- .001" or +/- .0001" or somewhere in between??

 

[guntech]

The bolt with the excessive play is where to start... wrap a piece of thin tape around the middle of it... try sliding that through the action now... measure...

 

[trevj]

Use whatever material you can get the best surface finish on, and is cheap.

Pin Gage's are usually very close tolerance to specific sizes, and typically hardened, ground, and lapped to as near perfect as the customer is willing to pay for ( decimal places in the tolerances, cost a lot for each one you want added).

For a plug gage that is simply to measure the bores in the action, you are likely not ever going to use them again, unlike a manufacturer, who wants tools that will last a long time, even in unsympathetic hands, which is the polite way of saying, they have to hand the stuff over to guys that can f**k up an anvil with a rubber hammer if they are not watched continuously.

Or you could just buy some expanding bore gages, and learn how to use them. Or inside calipers.

 

[joehunt]

I would say to use material that is going to closely match the new bolt. A piece of soft aluminum with a poor surface finish is going to bind long before a ground, hardened piece of tool steel. I’m not sure anything less then a full length gauge would be a good choice to make a decision on the new bolt size. Bore gauges and inside calibers will not take into account how straight the bore in the action is or the tight spot that you missed.
As a side note I’m not sure you should not buy a firearm sight unseen based on a savage have excessive clearance around the bolt.
I don’t know how much clearance your talking but they are low cost mass produced firearms.
Joe

 

[mooncoon]

For a plug gage that is simply to measure the bores in the action, you are likely not ever going to use them again,

Or you could just buy some expanding bore gages, and learn how to use them. Or inside calipers.

Off original topic, but I have made a number of stepped plug guages out of scraps of barrels. They are handy for barrels with odd numbers of grooves. I have some expanding bore guages with a ball shaped end but use the plug guages far more often. For pin guages I would use a steel which is free machining and most likely to give you a smooth surface

cheers mooncoon

 

[trevj]

Off original topic, but I have made a number of stepped plug guages out of scraps of barrels. They are handy for barrels with odd numbers of grooves. I have some expanding bore guages with a ball shaped end but use the plug guages far more often. For pin guages I would use a steel which is free machining and most likely to give you a smooth surface

cheers mooncoon

Yeah, barrel steel, by default, needs to be pretty easy machining material.

And, it has a nice hole in the middle (or near enough, seen some pretty off center barrels!) already.

Honestly. for the OP's purpose, I'd grab whatever higher temper Aluminum was handy, and make a plug gage about an inch long, and have at it. Chuck them back into the pile after.

The reason I say High temper is that the -T0 and -T3 tenmper aluminum tends to machine a little like warm chewing gum. -T6, especially 7075, and 6061, tends to be a lot easier to get a finer finish, and, if you set it up well, you can start a bit oversize and skim very fine cuts off to come down till the plug fits, rather than dicking about making a dozen different ones.

 

[tiriaq]

Exactly. Start oversize, and take light cuts until it fits nicely into the receiver. Once you have a smooth sliding fit, measure and order the new body.