Rifles With Long Chambers

This post describes shooting experiences with rifles that have (too) long chambers.  Can poor performance be expected?

Nature News

Spring was very late in coming to ATOTT headquarters after a brutal winter, but this little Dutchman’s Breeches proves that it finally came.  This shy little guy springs up every year at the base of a tree next to our steps, and when it arrives, I know spring has sprung.

Dutch Britch adjst

Down to Business

If you are a rifle enthusiast and work with a variety of rifles over a period of time, chances are good that you will at some time encounter a rifle with a long chamber.  Many shooters think that the condition results in poor shooting performance, which makes them want to sing the blues*.

Considering the various parts of a cartridge and its fit in a chamber, the term “long chamber” is open to misinterpretation.  I will be careful to say that what I am talking about is the “throat,” or, length of the bore in front of the case neck before the rifling engages the bullet.  That region is properly called the “leade,” and if it is longer than necessary the chamber has “free bore.”  The practical result is that the fired bullet must travel a distance before it engages the rifling.

Savvy shooters think that a well-seated bullet should be close to the rifling (lands) when a cartridge is correctly chambered.  A distance of 0.02 – 0.03” might be suggested, and some talented target shooters even want their bullets to touch the lands at firing.  This practice has a long and distinguished history in target shooting, going back to black powder match days.

However, owing to manufacturing process, whether intentional or not, a finished chamber may place the bullet in the range of 0.25 – 0.50” from the lands.  Then you have a long chamber.  I have a suspicion that some rifle makers add free bore to certain models in certain chamberings as a safety factor, and that the practice is more common than we might think.

[It is well-known that Weatherby rifles for the Weatherby cartridges are made with long chambers by design in order to handle the huge powder charges with a bit more safety.  The chambers have about 3/8″ of freebore.  Some folks have felt that the condition contributes to a lack of gilt-edged accuracy for Weatherby cartridges but, read on]

The Blues

Two unwelcome results are often attributed to long chambers:

Lower than expected bullet velocity.  Upon firing, pressure builds at a slower rate and to a lower ultimate maximum when the bullet is initially unimpeded by the rifling.  Lower pressure means lower velocity.

Accuracy less than desired.  When travelling across the free bore, the bullet does not have adequate support.  A degree of wobble may be introduced, the effect being a loss of accuracy.

A Good Example

Recently, I glass bedded a Remington Model 788 action in a Ramline plastic stock.  I test fired the result for velocity and accuracy with a variety of ammunition, and I posted the results, which were pretty good.  This rifle, however, has a long chamber.  How do I know?  I measured it using a Stony Point overall length gauge.  This handy product is now sold by Hornady.  Using a Hornady 165-gr flat base spire point bullet the gauge showed that the OAL was 3.02.”   Hornady recommends a COL of 2.75” for this bullet in .308, a difference of more than one quarter of an inch.  The length shown by the Stony Point Gauge would not work in the box magazine of the 788.  Now that is a long chamber.

Long .308:  Chamber cast, top.  OAL Gauge, bottom.

Long .308: Chamber cast, top. OAL Gauge, bottom.

My rather crude chamber cast gave visual proof of the condition.  Measuring the cast showed that the case neck length is about .02” longer than the nominal length of 0.304” taken from the diagram in Hornady’s reloading manual.  This margin provides good safety, but is not excessive.  Note also that it takes about a quarter of an inch for the lands to reach full depth from where they begin.  The lower image is the Stony Point Case Gauge with the Hornady 165-gr bullet, showing where the bullet needs to be seated in order to touch the lands in this long chamber.  Not much of the bullet base is actually in the case neck

Shooting Results

Velocity results with this rifle depend to some extent on bullet weight.  Loads using 150 or 165-grain bullets with IMR 3031 or Hodgdon Varget have given velocities about 100 fps lower than predicted by loading manuals.  On the other hand, Winchester and Federal factory loads using 180-grain bullets have given velocities consistent with listed values.

This does not allow me to generalize about velocities from long chambers, other than to say that a long chamber will probably show sub-standard velocity with some bullets.  I am tempted to say that velocity falloff is greater with the lighter bullets because the chamber length overage is less with the heavier (therefore longer) bullets.  More data is needed.

Accuracy results were also mixed.  Remington, Winchester, and Federal factory ammo was fairly uniform in giving groups in the 1 -2″ range, with some tendency toward one flier in a three- or four-shot group.  This performance would be acceptable for hunting, although not as good as I would expect for a good .308 sporter.

Carefully assembled handloads, however, gave much better performance.  I offer in evidence a target showing six, consecutive three-shot groups at fifty yards that measured an average 0.39″  (0.78 MOA).  The load used 42.6 grains of Varget to push a Hornady 165-gr SP.  Yes, they are only three-shot groups, but when you find this level of uniformity, with little tendency toward fliers, you can be sure that rifle and load are working very well.  Handloads using Varget or IMR 3031 with 165-gr bullets generally performed better than factory ammo.

Target adjusted

So, again, I probably should not generalize, but I would say that a long chamber will not always give you an accuracy penalty.

Other Examples

This 788 is not the only long-chamber animal I have worked with in my shooting life.  Another good example is a Savage Model 340, a bolt-action .30-30.  Its chamber measured 2.846″ with the Stony Point Gauge (Sierra 170-gr Bullet), almost a quarter of an inch longer than the nominal length of .30-30 ammo.  I will compare this rifle’s performance to that of a Remington Model 788 in .30-30 Winchester.  Its measured chamber length is 2.546.”  Some years ago I did and extensive test of factory ammo and both guns were included.  With seven different factory 150-grain loads the 340 averaged 90 fps lower velocity than the 788 (both 22-inch barrels).  With six different 170-grain loads the average velocity difference was 60 fps lower for the 340.

Moving along to an accuracy comparison, the average 4-shot group for the 340 with 150-gr loads was 1.80 MOA, only 0.20 MOA larger than the 788’s average group.  The difference was a bit greater, about 0.40 MOA, for 170-gr loads.  We must not, however, pin this accuracy difference entirely on the 340’s long chamber.  There are many other factors affecting accuracy.  In general, we would expect a Remington 788 to be more accurate than the economical Savage 340, regardless of chamber length.  We think about the quality of the barrel, chamber machining, and action bedding, for example.

Finishing my thoughts on the 340, I can say that it has often given very good accuracy with handloads.

Other examples that I could give include a Remington Model 700 .222 Remington and a Ruger No. 3 .30-40.The Model 700’s chamber was so long that a 52-grain match bullet set to touch the lands would not be in the case mouth at all.  Loading manual powder charges gave lower velocities, but groups as small as 0.60 MOA were common with this riflle.  Regarding the .30-40, I don’t know about the Ruger No. 3, but older Krags were throated for the 220-gr military bullet, so such chambers will be long for 180-gr and lighter bullets.

Conclusions

The picture shows a dummy cartridge (right) with bullet seated to be within 0.02″ of the lands in my 788.  This I wll not be doing.  The round is way too long for the magazine.

Cartridges adjusted

Rifles with long chambers are individuals, as are most rifles.  You may have one that shoots so well that you would never suspect that there was anything odd about it.  Ignorance may be bliss.

Typically, you will find somewhat lower velocities.  You will not necessarily find accuracy problems traceable to the chamber length, and accuracy may be exceptionally good in spite of the condition.

 

 

 

*My speeds are slowing,

My groups are growing,

The more I shoot, more tears are flowing,

The clouds are dark, there’s no good news,

I got the old, long-chamber blues.

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