Chamber depth

[Charlie Diehl]

I have a 28 ga Parker vintage 1917-18 with a chamber depth (?) of 2-3/4” and need to know if I can use 2-3/4” RST shells. I based my assumption of chamber depth on the fact I measured from the breech to a definite ridge in the bore that can be felt as well as seen. After reading about chamber depths and the use of gauges to do so I am wondering if I may have measured incorrectly as it appeared maybe “too simple”.

[Dave Noreen]

At the time your gun was made, our North American Ammunition Companies were offering 28-gauge shells in two lengths. The "standard" shell was 2 1/2 inch, and carried a load of 1 3/4 drams of bulk smokeless powder or 14 grains of dense smokeless powder such as Infallible or Ballistite, pushing 5/8 ounce of shot. A longer shell of 2 7/8 inch with a slightly hotter load of 2 drams of bulk smokeless powder or 16 grains of dense smokeless powder such as Infallible or Ballistite, pushing the same 5/8 ounce of shot was also offered.

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With Parker Bros. policy of holding chambers about 1/8 inch shorter than the intended shell, a 2 3/4 inch chamber would be about right for the 2 7/8 inch shell.

The progressive burning powder, high velocity, 28-gauge load with 3/4 ounce of shot was introduced in a 2 7/8 inch shell in the 1931-32 time frame.

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The 2 3/4 inch 28-gauge shell first appears as Skeet loads, just before WW-II. Shortly after the War the 28-gauge was standardized at 2 3/4 inch.

Whether your gun was rechambered to 2 3/4 inch at some time or came from Parker Bros. with longer chambers may be impossible to prove.

[Charlie Diehl]

Dave, thank you. Can you help me with determining if I have measured the bore correctly? I can shine a light into the breech and see a definite ridge. I can also insert a very thin metal blade into the breech and it hits this ridge at a depth of 2-3/4”. After reading many posts concerning chamber depth measuring methods am I accurately measuring the chamber depth? I have been using a 2-1/2” RST shell with 5/8” of shot and assume that if I use a 2-3/4” shell with 7/8 oz of shot I would improve my chances of hitting quail.

[John Dallas]

Be careful. A chamber measuring 2 3/4 is for a 2 1/2" shell. Remember - Shell length is measured as unfired. When it is shot, it opens up about another 1/4"

[Charlie Diehl]

John, thank you for your response. Am I correct in assuming the bore is 2-3/4” based on the method I used to measure it? Many other posts I have read on this subject suggest it is very difficult to determine chamber depth.

[John Davis]

Be careful. A chamber measuring 2 3/4 is for a 2 1/2" shell. Remember - Shell length is measured as unfired. When it is shot, it opens up about another 1/4"

I believe that is a misstatement.

[Charlie Diehl]

John, thank you for your comment but now I am even more confused.

[John Davis]

A 2 3/4 inch shell when loaded measures approximately 2 1/2 inches. When shot it measures 2 3/4 inches. Parker chambered their guns 2 5/8 inches to shoot 2 3/4 inch shells. The thought was that the 1/8 inch overlap created a better gas seal.

[Garth Gustafson]

Charlie, Galazan (Connecticut Shotgun) sells a combination chamber length and choke gauge tool that is fast, easy to use and 100% accurate. It handles all gauges from 10 to .410. Its a wise investment at $45. There may be other less expensive ones out there too.

[Charlie Diehl]

If I encountered a shoulder 2-3/4” from the breech using the very simple method of inserting a small metal ruler, have I accurately determined that my 28 ga Parker has a 2-3/4” chamber? Based on this measurement can I use a 2-3/4” shell which would allow me to shoot 7/8 oz of shot instead of 5/8 oz of shot?

Why have so many members comments for years regarding chamber measurement methods make it sound complicated IF the manner by which I determined chamber depth is accurate?

[Dean Romig]

I just measured my 1908 28 gauge on the 0-frame at 2 1/2" from the bottom of the rim recess to the beginning of the forcing cone.

I also just measured my 1924 28 gauge on the 00-frame at 2 1/2" from the top of the rim recess to the beginning of the forcing cone.


My best guess is that if a 1917-18 28 ga. Parker has 2 3/4" chambers it was specially ordered that way or the chambers were lengthened at a later date... but by whom?

I am a firm believer that anyone involved with classic old SXS guns should have one of these Galazan tools with him at gun shows as well as in his gun room.

{Disclaimer} the attached choke gauge is virtually useless as it is merely a guide and will NOT give you the true constriction measurement in thousandths of an inch.... which is the definitive way to determine choke.


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[Garth Gustafson]

Everybody has their opinion and there are different ways to do it. I’ve tried measuring my chambers using the trimmed index card approach but that didn’t work well for me. It sounds like you’re satisfied with your result and I wouldn’t over think it.

But have your barrels inspected and the wall thickness measured by a knowledgeable gunsmith who is familiar with these old doubles. We don’t know if your chambers were lengthened after leaving the factory and if the wall thickness was compromised.

[Charlie Diehl]

Garth and Dean. Thanks for your posts. I am not necessarily certain that I have measured the chamber depth correctly. That is why I have asked for comments and suggestions. I do not have instruments to measure or detect any taper. I have simply measured into the point where I encounter a shoulder 2-3/4” from the breech that implies the bore diameter for the first 2-3/4” is larger than the bore diameter beyond the shoulder.
I have another 28ga Parker (vintage 1905) that has no detectable shoulder inside the bore and that would make it more difficult to determine actual chamber depth.

[Bill Murphy]

Yup, John Davis is correct in mentioning that John Dallas's statement was incorrect. In Parker terminology or practice, a chamber measuring 2 3/4" is meant for a 2 7/8" shell or shorter. Of course, the 2 7/8" shell is no longer loaded, but in the twenties to the late forties, it was loaded and Parker guns were made to shoot it. Your gun could have factory 2 3/4" chambers.

[Bruce Day]

Have you reviewed the Sherman Bell Double Gun Journal articles which determined that there was approximately a 3-5 percent increase in chamber pressure from shooting shells 1/4 “ longer than than chamber length?

Is your gun so infirm that this extra pressure is likely to bulge the chamber ? Do you intend to shoot SAAMI max pressure shells so that the extra pressure could harm the gun ?

You asked if moving to a shell with more shot would help you hit more quail . That would help you kill more quail but not hit more. A 28 ga is marginal in killing load anyway , and the long shot string does not help. Shoot some sporting clays and the pattern deficiencies become apparent.

My friends who come out here and hunt high plains quail in the wind , many of them bring a 28 ga but it goes back into the truck by noon. Plantation quail or released birds I think it would be well suited for that. These birds ran out and flushed at 25 to 30 yards so that the shots were 40 yards.

[Charlie Diehl]

Thank you Bruce.

[Dean Romig]

Is your gun so infirm that this extra pressure is likely to bulge the chamber ?


Now there's a loaded question.... no pun intended.

We can't 'know' the answer to that question without examination of wall thickness by an expert in the field - a qualified double-gun smith. And then it would be his opinion subject to conjecture.

IMO, unless it can be proven that the chambers were cut to 2 3/4" by the manufacturer it should not be shot with anything other than 2 1/2" shells loaded to manufacturer's specs at the time of production.

We need to be sensible in these matters.





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[Charlie Diehl]

Thanks Dean. Agreed!

[charlie cleveland]

at present we will have to be carefull the 28 gauge shell is being loaded in a 3 inch shell...charlie

[Dave Noreen]

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[Dave Noreen]

This has been my canned response for years on the chamber depth question.

Chamber depth is considered to be the distance between the breech end of the barrels and the joint between the chamber body itself and the forcing cone, which reduces down to bore diameter. This is loosely based on the length of the "Fired" shell. Today, theoretically when the crimp opens on the shell being fired the end would land at the junction of the chamber and cone. Prior to WW-II many companies had the practice of holding the chamber about 1/8 inch shorter than the shell for which it was intended. Fly in the ointment is nominal measurements often differ from actual ones in both chambers and shells. A very good method I have found of measuring chambers without much outlay of cash, and is quite accurate enough for virtually any situation, is a common 6" flexible machinist's scale which you likely have. Hold the barrels with muzzles toward a light source, not necessarily a concentrated one a window is great, while looking into the breech and the cone will be thrown in a shadow. May have to move the barrels around a little until it is distinct. While still looking into the chamber simply slide the scale in until you observe the end coming flush with the shadow line & mark position of breech end with your thumb. Remove and read the scale. I usually repeat this a few times to insure I am getting a consistent reading, but you will be amazed how accurate this can be done. While I own a Galazan chamber gauge, I use this more often than not. The chamber body itself has a taper of about .005" per inch. Sometimes chambers were cut with slightly worn reamers giving a slight undersize chamber. If the chamber is a bit undersize a gauge made to "industry" standards will not go in to the true depth of the chamber. A.H. Fox Gun Co. shotguns are known for having tight chambers. The machinist’s scale method can be more accurate.

Sounds to me like you did it right.

[Charlie Diehl]

Thank you Dave. Very helpful.

[Bruce Day]

Here are the Parker recommended loads from the time your gun was made. I suggest that adherence to these standards is more important than a potential 1/4 “ in expanded cartridge length in some shells.

A 7/8 oz load was either a 20 ga or 16 ga load but not for a 28.

[Charlie Diehl]

Thank you Bruce

[Frank Srebro]

This has been my canned response for years on the chamber depth question.

...…….. Prior to WW-II many companies had the practice of holding the chamber about 1/8 inch shorter than the shell for which it was intended. .

Just recently while prepping for an article I found an excerpt from a 1920 dated letter from W.A. King that stated, in effect, that Parker chambers were bored 1/8" short for the intended length shell, and furthermore that Parker had succeeded in getting even better distributed patterns with increasingly more than 1/8" overlap into the cone, to the point where the fronts of the fired [paper] shells were torn and ragged. The King letter also stated that latter practice was not recommended.

Readers please note that progressive burning powders weren't widely introduced for heavy shotgun loads until about 1922.

[Bruce Day]

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