Straight Stock and Pitch

Austin W Hogan · 12-17-2009, 04:33 PM

There is nothing like a good problem to keep one inside and busy on a sub zero day. I think I have figured out the geometry of pitch. A diagram and explanation are attached.

The pitch table indicates that 3.5 +/- 1inch is the common value for Parker field gun pitch as measured by the wall method. I made up a geometric diagram based on common Parker dimensions; 30 inch barrel;14 1/4 inch pull;2 3/4 inch drop at heel(dah); 1 5/8 inch drop at comb(dac) ; and 3.5 inch pitch. I measured several 12ga Parkers and found the arc of the trigger to be 2 inches behind the breech, and the comb to be 7 inches behind the breech.

This diagram determined that the Parker heading up and butt plate tooling for machine inletting and carving stocks was set up to cut the butt at an angle of 1 : 8 relative to the breech. That is 7.2 degrees relative to the breech face, and 82.8 degrees relative to the rib. That cut provides 3.5 inches of pitch for the standard dimensions noted above.

Changes in dah cause a 1 inch change in pitch for each 1/2 inch change in dah. Changes in barrel length cause a 1/8 inch change in pitch for each inch change in barrel length. Changes in pull change pitch 1/16 inch per inch change in stock length. All of these changes in wall pitch occur with constant pitch angle at the butt; ie they produce no change in "feel".

Pitch as such does not influence recoil against the face; this is the result of slope of the comb due to difference dac - dah. A monte carlo can provide dac - dah = 0 for no face recoil, while keeping a lower dah for faster mounting.

Best, Austin

Harry Collins · 12-17-2009, 05:04 PM

Austin,

That is a clear way of tying all the pieces together. Even I understood. I couldn't find your artical in the latest DGJ Index and Reader. I will look in the first one and then in those DGJ's not indexed. Pitch has been a wonderful topic of discusssion. I have had Winchester Model 12's with negative pitch and have not been able to check the current Winchester residents. Will try to do that this evening.

Thanks, Harry

Austin W Hogan · 12-17-2009, 05:31 PM

Thank you Harry. I have a Fox trap with negative slope on the comb, and a VHE trap with BTFE and a monte carlo with 0 slope ( dac = dah) on the comb. Both guns feel recoiless with any load.

Best, Austin

12-17-2009, 05:50 PM

[QUOTE=Harry Collins;9312]Austin,

That is a clear way of tying all the pieces together. Even I understood. I couldn't find your artical in the latest DGJ Index and Reader. I will look in the first one and then in those DGJ's not indexed. Pitch has been a wonderful topic of discusssion. I have had Winchester Model 12's with negative pitch and have not been able to check the current Winchester residents. Will try to do that this evening.

Thanks, Harry- Let me know if I can help, as I have seven older Model 12's-one a 20 made in 1932 with the pre-1935 "perch bellied" stock and smaller grip, a 28 made made in 1939, two 3" Magnums, a Field grade 12 and a original 1948 era Pigeon Trap 12 30" VR-- be glad to give you aprox. pitch, as none of them have been altered. I am blessed, right handed, right master eyed, still 20-20 vision, and any unaltered Model 12 field gun fits me "to a Tee"- But I shoot the doubles a great deal, possibly some variance between them, all I know is, if the stock is not too short, and I see nothing but the single bird in my focus and not any rib or sight bead(s)- dead bang!!

Austin must have an engineering background, and the genius of the Parker designers is evident to us all in setting a standard for pitch that allowed for slight variances in drop and LOP- interesting that Austin detailed for us the data from the front trigger arc position- wonder if later on when Parker offered its single trigger as an option if that placement changed things??

Bill Murphy · 12-17-2009, 08:05 PM

Yup, Harry, the first generation Model 12 stock was made with negative pitch and no one complained. When the second generation Model 12 stock was designed, it had positive pitch and no one complained. I was raised on the first generation Model 12 stock and shot it very well. What did I know?

Harry Collins · 12-19-2009, 09:28 AM

Both Winchesters have positive pitch. The 97 was made in 1944 and the 12 was made in 1962. I was never able to find Austin's artical on pitch in DGJ.

Harry

Austin W Hogan · 12-19-2009, 02:23 PM

Harry; I am not sure of the issue, but the last draft was March 07. I need to compress the table to post it here in the FAQ. Send me a message at austin.w.hogan@valley.net, and I will send you the stock dimension table.

Merry Christmas,

Austin

Bindlestiff · 12-19-2009, 03:10 PM

Quote:

Originally Posted by Austin W Hogan

Harry; I am not sure of the issue, but the last draft was March 07. I need to compress the table to post it here in the FAQ. Send me a message at austin.w.hogan@valley.net, and I will send you the stock dimension table.

Merry Christmas,

Austin

Austin, I tried to attach your data table on this thread as a PDF file for viewing. I had to hide a column to get it to fit, the notes can't be seen but I think the real data is there for you to see.

Robin