I have been shooting a GPR in 50 cal. for about six months now. I read the forum religiously but understanding how to determine patch thickness is something I have not seen discussed. Everyone mentions .010 or .015 or other thicknesses but no where have I seen anyone explain how to determine thickness. I see people buying pillow ticking in various thicknesses but how do you know the thickness when buying it? I can't imagine you just walk into Joanne's Fabrics and ask for .010 pillow ticking or do you? Also does the thickness change after washing? Can someone help me understand this? Thanks.
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Patch thickness
- Thread starter topbike
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Measure it with calipers or a micrometer.
Don Steele
45 Cal.
Carry a decent caliper with you into the store. Explain to the folks working there what you need...e.g.: 100 % cotton, or flannel, or blue-stripe "pillow ticking", light canvas...whatever...then measure the thickness. It's been my experience that fabric bought off the bolt will need to be washed at least once...maybe more before the thickness will settle down.
It is a hard thing to master for me at least. Caliper or Mic I have a hard time getting the readings others or the factory do.
My GPR does best with .018 thickness pre cut patches from OX-Yoke with the .490 ball. With the .495 I use the .015's.
The 54 barrel does the same with the .530 and .535. I hope this helps. Geo. T.
My GPR does best with .018 thickness pre cut patches from OX-Yoke with the .490 ball. With the .495 I use the .015's.
The 54 barrel does the same with the .530 and .535. I hope this helps. Geo. T.
Getting a good feel when measuring the thickness of a soft squishy thing like cloth is difficult.
If a person is saying they can measure the thickness to the nearest one thousandth of an inch IMO they are just fooling themselves.
My suggestion is to use a dial (or digital) caliper. ( The screw type micrometer can also be used if it has the little friction drive knob at the end of the rotating spindle).
Rather than placing the material between the two relatively sharp jaws which can cut down into the soft cloth, place the material further into the jaws so about 1/2 inch is laying on the opposing flats.
Yes, the cloth will still be compressed by the jaws but getting a fairly consistant reading will be easier.
As for how hard to compress the material my suggestion is, if you have a factory patch that you like and the maker said it was a ".015 thick patch", use your calipers to measure its thickness. Once this is done, remember how hard you were forcing the two jaws together and remember the thickness reading your getting now.
It might not be .015 but you already know that whatever it reads, it's the same as what you've been using in the past.
When you get to the cloth store, use the same pressure on the jaws and look for the same reading you got with your old patch.
If a person is saying they can measure the thickness to the nearest one thousandth of an inch IMO they are just fooling themselves.
My suggestion is to use a dial (or digital) caliper. ( The screw type micrometer can also be used if it has the little friction drive knob at the end of the rotating spindle).
Rather than placing the material between the two relatively sharp jaws which can cut down into the soft cloth, place the material further into the jaws so about 1/2 inch is laying on the opposing flats.
Yes, the cloth will still be compressed by the jaws but getting a fairly consistant reading will be easier.
As for how hard to compress the material my suggestion is, if you have a factory patch that you like and the maker said it was a ".015 thick patch", use your calipers to measure its thickness. Once this is done, remember how hard you were forcing the two jaws together and remember the thickness reading your getting now.
It might not be .015 but you already know that whatever it reads, it's the same as what you've been using in the past.
When you get to the cloth store, use the same pressure on the jaws and look for the same reading you got with your old patch.
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I have used both but prefer the mic with friction knob as it is very consistent each time and the anvils are flat faced disks which give very uniform compression readings. Mike D.
I agree. I use both (micrometer and digital caliper), but the micrometer gives the most consistent reading because of the ratcheting twist knob, which ensures a constant pressure is applied.
I know some advocate screwing the micrometer in hard, to give a compressed reading, but I see two issues with this - one is that the amount of pressure you apply could vary each time, and two I've been told that this is NOT a good way to treat a micrometer. So I don't do compressed readings.
As has been suggested, if you use digital/dial calipers then holding the cloth between the full length of the jaws gives a pretty accurate reading.
I know some advocate screwing the micrometer in hard, to give a compressed reading, but I see two issues with this - one is that the amount of pressure you apply could vary each time, and two I've been told that this is NOT a good way to treat a micrometer. So I don't do compressed readings.
As has been suggested, if you use digital/dial calipers then holding the cloth between the full length of the jaws gives a pretty accurate reading.
IMO think the reason that there's no hard fast rule that says 'how to determine' patch thickness is that different people have different needs (for hunting vs' serious target shooting) and usually end up with with what they like best for their needs through trial and error.topbike said:
Speaking for myself, I learned what worked best for my needs and interests simply by experimenting with patches of different thickness, for the .010" under bore size balls that I choose to use.
I also learned that you can't simply do the math...ie: a .490" in a .500" bore leaves .010" clearance, and math alone would suggest a .005" patch...coming up on both sides taking up that .010" space would be right...except that it doesn't actually work that way because cloth compresses...and you want / need it to for good accuracy. Experimenting showed me that an .018" patch with my .490"s in a barrel with square grooves actually gave me excellent accuracy for my needs and was thick enough to carry good lube into the bore, etc.
Correct, at least that's been my experience...the counter clerks have no idea about their cloth thickness in thousandths of an inch, and like other have mentioned, I take my dial calipers with me.
Yes, my experience has been that with fairly thick material it'll usually draw up in the neighborhood of .002"-003" thicker.
I just bought a bolt of pillow ticking at Jo-Ann Fabrics last week as I needed a finished thickness of around .024"-.026" to make a few thousand patches from.
Jo-Ann's had a 10yd bolt of blue & white ticking that measured .025" in the store, and I knew it would probably wash / dry / iron flat to be slightly larger around .027"-028" and it did, finishing up at .028"...and has range tested perfectly.
On the subject of measuring technique:
I first sample measured some patches from bags of OxYoke .018" pillow ticking and found that the .018" measurement occurred just when the jaws of the calipers met resistance of the material, not from compressing it. As a result that's how I've measured mine for 20 years now and it works fine for me. I simply roll the caliper jaws back and forth lightly feeling that same resistance each time on a full bite of material...at a few different areas of material...to get a sense for the average thickness and uniformity.
Don't know the groove depth in a .50 cal. GPR bbl, but for determining a patch thicknees, here's how I do it.
Let's use .50 cal bore dia. .and a groove depth of .012. So, .500 plus {.012 X 2=.024}=.524 groove dia. If a .490 RB is used, then .524 -.490= .034 divided by 2 =.017 minimum patch thickness which probably wouldn't fill the grooves, so I would use a .020 patch thickness.
Some wash the fabric and some don't....I usually don't.
A .020 patch thickness is fairly common in precuts, but if you're making your own, buy from a fabric store or a fabric dept. of a larger store. I prefer to use a micrometer when measuring fabric thickness and you can use either a light touch on the mike's thimble or if your mike has a "click" thimble, use it.
As you no doubt know, synthetics aren't used...cotton and linen are 2 good choices......Fred
Let's use .50 cal bore dia. .and a groove depth of .012. So, .500 plus {.012 X 2=.024}=.524 groove dia. If a .490 RB is used, then .524 -.490= .034 divided by 2 =.017 minimum patch thickness which probably wouldn't fill the grooves, so I would use a .020 patch thickness.
Some wash the fabric and some don't....I usually don't.
A .020 patch thickness is fairly common in precuts, but if you're making your own, buy from a fabric store or a fabric dept. of a larger store. I prefer to use a micrometer when measuring fabric thickness and you can use either a light touch on the mike's thimble or if your mike has a "click" thimble, use it.
As you no doubt know, synthetics aren't used...cotton and linen are 2 good choices......Fred
Thanks everyone for your responses. I have calipers and thought about measuring the material but was concerned about the amount of pressure to put on the material. Now I see that it is relatively subjective based on a known patch thickness that provides the best accuracy. Now it is starting to make sense to me so it appears that a trip to Joanne's Fabrics is in order.
I read the Forum religiously and appreciate the willingness of the members to share information.
I read the Forum religiously and appreciate the willingness of the members to share information.
topbike said:
Don't get hung up on numbers. What works for you is what you need. However, you do need a starting point. For that I use a micrometer that has a racheting release giving me consistent measurements at the store. My reading might be different than the next guys with a different mic. but if it works, it works.
Do do as advised, wash your material before use.
To determine if a patch thickness is (probably) right for your bore/ball combo take a fairly large hunk of the material, lubed on the side touching the bore, put a ball on the material and seat about one inch into the bore. Then pull out and examine the ball. If it went in with only moderate resistance and the ball shows rifling and patch weave you (probably) have a good fit. To get rid of the "probably" issue, spend time at the bench shooting groups at 50 yards. This is how it is done. If your groups are not satisfactory, you need to test with different, or thicker, patching and/or a larger ball. Of course, charges come into play with this process.
It takes time, powder, lead and patience. That is the game. Enjoy.
