Patch thickness and Pressure

[Trench]

Can any one tell me if an increase in patch thickness has an appreciable affect on chamber pressure and velocity?
I have a traditions .50 hawken. I originally went with 60gr of FFg, .49 ball and a .015 linen patch. This year I began shooting .018 pillow tick patch and 70gr of powder and noticed tighter groups. 2 inches at 75 yds.
I noticed the rifle kicked a bit more than it did when I tried 70gr and the .015 patch.
Then, I decided to try 70 gr of FFFg behind a .018 pillow tick and the rifle kicked like a mule (I came home with bruises) and not a single ball hit my 16x16 paper target at 75yds in a five shot string. I believe they were hooking to the right. Would going with a thinner patch when using FFFg increase accuracy and lower chamber pressure?
Any comments on what may be happening here?

 

[playfarmers]

Use what works. In my .50 Deerstalker, I use 80g of Pyrodex RS, a 15th pillow ticking patch, and a felt over powder wad to protect the patch. If I don't use a wad over the powder to protect the patch, the patches where blown, and accuracy is poor. The rifle hated 3f, but my .54 Trade rifle loves 80g of 3f, but I still use the over powder wad.

 

[brain]

3f ''burns'' ~10% hotter than 2f. so your 70 grn load of 3f was a hotter load.

the tighter ball&patch combo will help in getting a tighter group(my target load is a .495 ball wrapped in an .018 patch).
i assume the tighter combo would tech raise pressures, but nothing to write home about.

 

[Old Sarge]

Remember...if the patch is too tight...it may be cutting on loading, hence the lost accuracy. If you have to really hit the ball starter, it may be too tight. Good Luck.

 

[CoyoteJoe]

I doubt any pressure measuring device is even accurate enough to detect the difference between .015" and .018" patches. Now the difference between double F and triple F is very noticeable and I think it is considerably greater then the 10% figure which has recently been thrown around. In any case, your rifle is more than strong enough for the loads you are shooting.

 

[brain]

which is why you should recover fired patches to see what they have to say, while building loads.
i've made a habit of checking a few everytime it goes out.

 

[Runner]

Patching that works fine with 2f may burn thru and fail under the added heat and stress that 3f produces. The answer may be as simple as that. 3f does produce a lot more recoil than 2f does. In my 12 guage, the difference is pleasant recoil to that hurts. Try a wad under the patch if you really want to shoot 3f.

 

[longcruise]

Can any one tell me if an increase in patch thickness has an appreciable affect on chamber pressure and velocity?

FWIW, here are some actual chronographed observations that I've done over the years. First, a TC .54 Hawken with 28" barrel and a Lyman .54 GPR with a 32" barrel were compared side by side over the chrono loaded with identical components. The powder charge was 100 grains of Goex ff.

The TC 28" gun shot a bit more than 100 fps faster than the 32" GPR.

The only difference between these two guns was that the TC had a smaller bore. It was easily noticeble when loading. My conclusion was that the tighter bore produced higher pressure and velocity despite it's shorter length.

Another comparison was a GPR before and after firelapping. The rifle shot the same components significantly slower after firelapping. Now, firelapping does not make much difference in bore size, if even measureable, but it does make a huge difference in the smoothness of the and therefore it seemed that pressurre and velocity were reduced.

Thicker patch = tighter load = higher pressure = higher velocity.

Smoother bore = less initial resistance to the forward motion of the ball = lower pressure = lower velocity.

Anyway, those are my thoughts on your initial question.